How do I fix "The IMAP command "APPEND" (to Sent) failed"?

kedzfam wrote:

"The IMAP command "APPEND" (to Sent) failed with server error: APPEND Server error" how do I fix this

Say what... command "APPEND"

old issue, new issue, what changed?

What is it you are trying to do and where?

You can try— Mail>Preferences> Accounts> Mailbox Behaviors> Sent Mailbox > Select "All Sent"

open the "Show Details"—

Use Connection Doctor in Mail on Mac - Apple Support

ref:

https://help.zoho.com/portal/en/community/topic/what-does-this-mean-and-how-to-solve-it-the-imap-command-%E2%80%9Cappend%E2%80%9D-to-sent-failed-with-server-error-append-failed

Writing an effective Apple Support Communities question

Is this a New Issue ? If Yes, what exactly changed on this computer ?

Is this an Old Issue ? If Yes, what actions has the user taken to fix this issue ?

Reliable , accurate, details and context will really help to pinpoint a possible solution.

https://help.yahoo.com/kb/SLN15241.html

kedzfam wrote:

I use Mac Mail on my iMac to manage my Yahoo! mail account. Suddenly, yesterday, I wasn't getting new email messages and also would get the error message The message "Test" could not be moved to the mailbox "Yahoo!" with smaller explanation The IMAP command "APPEND" (to Sent) failed... when I composed a new email. (New emails do send successfully, however.)

I used Connection Doctor -- successful connections to Yahoo! account every time, but no new mail, quit Mail and restarted it multiple times, restarted computer several times. Also, removed Yahoo! account and then added it back. Tried rebuilding Mailbox several times. Sometimes shows that it is receiving x number of messages, but they don't show up. At one point, ALL of my emails disappeared in Mail. Somehow they showed back up late yesterday, with the new messages, but I seem to be back at point zero with same problem.

I can view email on my iPhone and in my internet browser but really prefer using Mail to compose new emails and manage all of it.

If the test failed—You can try— Mail>Preferences> Accounts> Mailbox Behaviors> Sent Mailbox > Select "All Sent"

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On Monterey I would start here—

Mail issues in macOS Monterey

Open mail app select Mail>Preferences>Privacy  disable:

“Protect Mail Activity” / 

“Hide IP address” / 

“Block all remote content” 

Use Mail Privacy Protection on Mac - Apple Support

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The current stable release of Monterey is macOS 12.3.1

Keep your Mac up to date - Apple Support

https://support.apple.com/guide/mac-help/get-macos-updates-mchlpx1065/mac