Apple Mail on MacBook Air uses incorrect signature and SMTP server for Gmail

Dear Apple Support Team,

I am requesting technical assistance with an issue affecting Apple Mail on my MacBook Air (2020, Intel Core i3), running macOS Sequoia 15.8.2.

I have two email accounts configured in Apple Mail:

• Gmail: *** – personal account, using the signature “Gmail prywatny”.
• iCloud: *** – business account, using the signature “służbowy”.

Problem description

When composing a new message from my Gmail account, Apple Mail displays the correct Gmail sender address but automatically inserts the business signature associated with my iCloud account.

In some cases, the signature selection menu offers only the iCloud business signature, even though the personal signature is correctly assigned to Gmail.

I have also encountered an outgoing mail issue. Apple Mail attempted to send a message from my Gmail address through the iCloud SMTP server (smtp.mail.me.com). The server rejected the message with the error: “From address is not one of your addresses”.

Troubleshooting already performed

1. Verified signature assignments and default signatures for both accounts.
2. Checked email account and outgoing SMTP server configurations.
3. Tested both automatic and manually selected default sending accounts.
4. Tested Apple Mail in macOS Safe Mode, where the issue persisted.
5. Created a separate macOS user account and tested Gmail signatures successfully.
6. Backed up and attempted to regenerate signature configuration files, including AccountsMap.plist, without achieving a permanent fix.

Interestingly, when replying to messages received through Gmail, the correct personal signature is available. The issue primarily affects newly composed messages.

This suggests a problem specific to the Apple Mail configuration within my primary macOS user profile.

I would appreciate escalation to the appropriate Apple Mail technical support team and guidance on restoring correct account, signature, and SMTP server associations without having to create a new macOS user profile.

I can provide screenshots of the error and additional diagnostic information upon request.

Kind regards,

Maciej ***

[Edited by Moderator]