General Settings

Open the settings window by clicking the gear icon in the sidebar or going to Settings.

Theme

Choose between Light and Dark themes. The interface updates immediately when you switch. When dark mode is active, windows open with a dark background from the very first frame -- no white flash.

Language

MailCopilot supports 6 interface languages:

• English
• Russian
• French
• German
• Spanish
• Italian

Select your preferred language from the dropdown. The interface switches instantly without needing a restart.

Message Retention

Controls how long full message copies (HTML content, inline images, and attachments) are kept on disk. Open Settings > General and use the Keep full message copy for dropdown to choose a retention period. Older messages remain searchable through their headers and plain text — only the rich .eml file is deleted when the period expires.

Option	Duration
30 days	~1 month
90 days	~3 months
180 days	~6 months
1 year	365 days (default)
Forever	No automatic pruning

When you shorten the retention period, MailCopilot shows a preview of how many cached messages will be removed before applying the change. Messages on the server are never modified -- only the local copy is affected.

Default Email Application

Toggle whether MailCopilot is registered with your operating system as the default handler for mailto: links. When enabled, clicking a "Send email" link in your browser, terminal, or another desktop application opens the MailCopilot compose window with the recipient and any other parameters pre-filled (to, cc, bcc, subject, body).

Registration is opt-in -- MailCopilot does not claim the protocol unless you explicitly enable this toggle. On Linux the registration goes through the desktop file's MimeType declaration; on macOS through open-url; on Windows through the protocol entry under HKCR\mailto. You can revert at any time by toggling this off, or by changing the default email handler in your system settings.

When MailCopilot is launched a second time -- for example by clicking a mailto: link while the app is already open -- the existing window is brought to the front instead of opening a duplicate, so you only ever have one running instance.

Spell Checking

Spell checking is off by default. Turning it on downloads a dictionary file from an outside server (Google's), and MailCopilot asks for permission first -- every time a new language is added. This is deliberate: MailCopilot never turns on a dictionary you have not approved. The download itself is carried out by the browser engine built into the app (Chromium), reaching Google's server -- MailCopilot cannot cancel a request that has already started. If a download ever begins for a language you did not approve, MailCopilot notices and turns spell checking off again rather than leaving it silently enabled.

Enable Check spelling as I type to turn the checker on. Misspelled words are then underlined as you type, anywhere you can type -- Compose, Settings fields, and so on.

Choosing dictionaries

Once spell checking is enabled, use Dictionaries to add one or more languages. The list of available languages comes from the spell-check engine itself, not from a fixed list built into MailCopilot -- what you see depends on what this build of the app can actually offer. You can add several languages at once; all of them are checked against simultaneously. Each added language can be removed again with its Remove button. If Check spelling as I type is on but no dictionary has been chosen, spell checking stays off in practice -- a dictionary is required.

The number of dictionaries you can have active at the same time is capped; the current limit is shown next to the picker.

Download permission

The first time you add a language that has not been approved before, MailCopilot shows a dialog asking whether to download that language's dictionary, and names the outside server the file comes from. Nothing you type is ever sent anywhere -- the checking itself always happens on your computer; only the dictionary file itself is fetched.

• Choosing Download approves the language: MailCopilot remembers the approval and lets the download go ahead. The approval is remembered for that language going forward -- if the dictionary needs to be fetched again later (for example after re-enabling a language you approved before), it happens without asking you again.
• Choosing Cancel (or dismissing the dialog) declines: that language is not enabled, but the decision is not remembered as a permanent refusal -- you can add the same language again later and you will simply be asked again. Any other settings you changed in the same save are still applied; declining a dictionary download never blocks the rest of your changes.

macOS

On macOS, spell checking is owned by the operating system rather than by MailCopilot. There is no dictionary picker and no download permission dialog on macOS, because macOS does not download anything and ignores any language list MailCopilot might otherwise send it -- Settings explains this and shows only the on/off toggle. To change which languages macOS checks, go to System Settings → Keyboard → Text Input.

Correcting a misspelled word

Right-click a word that is underlined as misspelled to see a short list of suggested replacements, plus an Add to Dictionary item. Clicking a suggestion replaces the word; Add to Dictionary adds the word to your personal dictionary so it stops being flagged. There is currently no way to review or remove words you have added to the personal dictionary from within MailCopilot.

Tray Icon & Background Operation

MailCopilot can show an icon in your system tray. Show tray icon is on by default; its menu offers Open MailCopilot, New Message, Check Mail, and Quit, and while the icon exists, hovering over it shows the unread count in its tooltip -- up to 999, then 999+.

Close Window to Tray

Enable Close window to tray (off by default) to keep MailCopilot running when you close the main window instead of quitting it -- mail keeps syncing in the background and new-mail notifications keep arriving. Bring the window back by clicking the tray icon (or its Open MailCopilot menu item); use Quit from the tray menu to actually exit the application.

Choosing Quit does not remove the tray icon right away. MailCopilot checkpoints its local database before actually exiting, which is why there is a short delay -- normally well under a second. While it is shutting down, the tray icon's tooltip reads Quitting… and its menu shows a single disabled Quitting… entry in place of the usual options, so you can tell the application is on its way out rather than assume Quit only removed the icon. If a message was still being sent when you quit, it is not lost: MailCopilot sends through a local queue, so an unfinished send simply stays queued and goes out the next time you run MailCopilot.

This setting depends on the tray icon being successfully created, not on anything drawing it: on Linux, MailCopilot creates the icon even when no tray host takes it, so Close window to tray works whenever the icon object exists -- whether or not your desktop actually shows it. It has no effect only if MailCopilot could not create the icon at all (an empty or unreadable icon image, or a platform that refuses to construct one).

MailCopilot does not check whether your desktop really draws the icon before hiding the window -- that is the desktop's decision, not MailCopilot's; a note under the setting flags this for Linux. If the icon is never drawn, there is nothing to click, but hiding stays recoverable regardless: starting MailCopilot again brings the hidden window back to the front, whether the icon works, is drawn wrongly, or never appeared at all.

If notifications are enabled, the first time a close hides the window to the tray in a given session, MailCopilot shows a brief one-time notification confirming that it is still running in the background and that clicking the tray icon brings the window back.

If you ever close MailCopilot expecting it to sit in the tray and cannot find it afterwards, see I closed the window and now I can't find MailCopilot in the FAQ.

Unread Badge

While you have unread messages, MailCopilot shows a badge on the application icon -- a numeric badge on the dock (macOS) or the Unity launcher (Linux), and a dot on the taskbar button (Windows); the count itself (up to 999, then 999+) is available from the tray tooltip whenever a tray icon exists. The badge respects the same folders you excluded from unread counts in Folders settings.

Launch at Login

Enable Launch at login (off by default) to have MailCopilot start automatically when you log in to your computer. On Windows and macOS this registers MailCopilot as a login item with the operating system; on Linux it creates an autostart entry (a .desktop file) so your desktop environment starts MailCopilot at login.

The toggle records what you asked for; a note underneath it appears whenever the actual result does not match. If this platform or build cannot register autostart at all, MailCopilot tells you the setting has no effect here. If turning the toggle on failed, a note explains that autostart could not be registered and will be retried the next time you save. If turning it off failed, MailCopilot tells you the app will still launch at login and that removal will be retried automatically on the next save -- so you are never left thinking autostart is off when it is not.

TLS Certificate Trust

MailCopilot verifies every TLS certificate presented by your mail servers against both the built-in Mozilla certificate bundle and your operating system's certificate store. Trusting the system store as well means that security software that inspects TLS traffic (for example Kaspersky and similar antivirus products) and corporate proxies no longer break mail sync on Windows, macOS, or Linux -- MailCopilot recognizes the certificates these tools present as valid instead of rejecting the connection. Certificate verification itself is never weakened by this: a certificate still has to be trusted by one of these two sources, or explicitly pinned, to be accepted. If your operating system's certificate store cannot be read, MailCopilot falls back to the built-in Mozilla bundle alone rather than skipping verification.

Certificate change recovery

If a server ever presents a certificate that cannot be trusted -- for example it no longer matches a certificate you previously accepted, or a self-signed certificate changed after rotation -- MailCopilot shows The server presented a different certificate directly in the main window, not only during account setup. The dialog lists the server, the issuer, and the SHA-256 fingerprint of the new certificate.

Confirming works in up to two steps, so that what you approve always matches what is actually on screen:

• If the fingerprint has not been read yet, the main button reads Read the certificate. Click it to fetch the certificate from the server; its details then replace the placeholder in the dialog.
• Once a fingerprint is shown, the button reads Trust and continue. Click it to accept exactly the certificate displayed.
• If the server's certificate changes again between opening the dialog and confirming, MailCopilot refuses the stale confirmation and re-reads the certificate to show you the new details -- but the dialog's offer to trust was tied to the certificate it first showed, and re-reading does not renew it, so confirming again will keep failing the same way. Click Cancel to close this dialog, then let MailCopilot try the connection again; a fresh dialog with the current certificate will appear for you to confirm. Nothing is trusted in the meantime.

Choose Cancel at any point to keep the previous state instead. The same server will not show this dialog again more than once per minute. The dialog's offer to trust does not stay open indefinitely either -- if it has been sitting unanswered for a long time, confirming it can be refused; here too, cancel and wait for a fresh dialog to appear.

Reconfirming a pinned self-signed server after updating

Certificate pinning is now strictly enforced for certificates that fail ordinary chain verification: previously, pinning only compared fingerprints for certificates whose chain already verified normally, while self-signed and private-CA certificates -- the exact case pinning exists for -- bypassed the fingerprint check entirely. That gap is now closed. If you pinned a self-signed or private-CA mail server before this change, the pin on file may hold only a fingerprint without the certificate needed to actually verify it -- such a server will stop connecting after updating, and MailCopilot will show the certificate recovery dialog described above.

To fix this, reconfirm the certificate through that dialog: if the button reads Read the certificate, click it first to fetch the certificate, then click Trust and continue; if Trust and continue is already showing, just click it. This saves the pin together with the certificate itself, and sync resumes automatically. You only need to do this once per affected server. Adding or editing a pin manually in Settings cannot fix this on its own -- for a certificate that is otherwise untrusted (self-signed, or issued by a private certificate authority not already in your OS trust store), only the recovery dialog can grant it trust; see When to Use Certificate Pinning below for why.

Interception notice

After the first successful sync of an account in a session, MailCopilot checks once whether its mail server connection is being inspected by antivirus software or a proxy (the certificate is only trusted through the system store) and, if so, shows a notice such as "The connection to {{host}} is being inspected." naming the issuer when it is known. This check runs at most once per server for the lifetime of your profile, whether or not interception was found -- so if interception is turned on for a server after this one-time check already ran clean, MailCopilot will not notice it. The notice can be dismissed.

Certificate errors are retried on a long interval (6 hours) rather than the short interval used for ordinary network failures, since they require your decision and will not resolve on their own.

TLS Certificate Pinning

TLS Certificate Pinning adds an extra layer of security for your email connections. It ensures that your client only connects to servers presenting a specific certificate, protecting against man-in-the-middle attacks.

Managing Certificate Pins

1. Open Settings and go to the Accounts section.
2. Click Edit on an account to open its settings.
3. Scroll down to the TLS Certificate Pinning section.

The section shows a table of pinned certificates with their host, port, fingerprint, and the date they were added.

Adding a Pin

1. Click Add pin.
2. Enter the host (e.g., imap.gmail.com) and port (e.g., 993).
3. Click Fetch & Pin. MailCopilot connects to the server, retrieves its certificate, and shows you the fingerprint.
4. Confirm to save the pin.

A pin added this way only narrows which certificate is accepted for a server that is already trusted through the normal Mozilla bundle or your OS certificate store -- it does not by itself make an otherwise-untrusted self-signed or private-CA certificate trusted. For a self-signed mail server (or one from a private certificate authority not already in your OS trust store), adding a pin here is not enough to connect; you need to confirm it through the certificate recovery dialog described in TLS Certificate Trust, which is the only place MailCopilot grants trust to such a certificate.

Removing a Pin

Click the delete button next to any pin in the table to remove it. This only removes the saved pin -- afterwards, MailCopilot will accept any valid certificate from that server.

Adding a pin automatically reconnects to the mail server so the change takes effect immediately. Removing a pin does not reconnect automatically -- it takes effect the next time MailCopilot connects to that server.

STARTTLS servers (ports 143 and 587)

Servers reached over STARTTLS (typically IMAP port 143 or SMTP port 587, where the connection starts in plain text and upgrades to TLS) do not hand over their certificate at the point where MailCopilot captures it for pinning. For these servers only the fingerprint is stored, not the certificate itself -- so a self-signed or private-CA STARTTLS server cannot be made to connect this way; use implicit TLS (typically port 993 for IMAP, 465 for SMTP) if your server supports it.

When to Use Certificate Pinning

Certificate pinning is especially useful for corporate environments or situations where you need to verify that your email connections are going to the expected servers. For most personal use, the default TLS verification is sufficient.