I tried a few things, and the aerc behaviour seems fine. When I read an email, the “S” is added, and when I move it, the flag is preserved.

However, I observed 2 scenarios:

• If I read > mbsync > move > mbsync, the result is the expected one, having the mail red and moved on both server and locally;
• If I read > move > mbsync, the mail is red and moved locally, but it’s only moved on the server. This means that the next time that I do mbsync, the mail will revert to unread locally.

One thing I noticed (which might be the problem somehow?) is that:

• The filename is initially something like “1756379541.12762_13.host,U=13:2,”
• After the reading changes to “1756379541.12762_13.host,U=13:2,S”
• After the moving changes to “1756379541.12762_13.host:2,S”
• After the sync changes to “1756379541.12762_13.host,U=3376:2,S”
• And eventually, after another sync the S flag is removed

This means that the difference in the 2 scenarios above, is that in the first case (the expected one) the mail is synced while having the U=13 present, while in the second case is synced with the U removed.
I tried to understand what’s the meaning of that part (which looks like an ID) and if it’s relevant in the process, but I didn’t find any information, sadly.

For now, I think I will just use the imap connection rather than local, but if you have any insights, please let me know! 🙃 And thanks again for the debugging tip, it really helped to understand what’s going on! :D

Thank you very much the info! I was looking for something like this, but eventually I failed 😆
I’ll try as soon as I can and get back with the result!

Great, thanks! I’m quite sure it could be beneficial for everyone, I’ve been doing kinda of heavy research lately and I’m still confused about where to do what :D

I’ve got pwned by the bot