[neomutt-users] Neomutt closing IMAP connections during mail download/querying

[Jonas Tobias Hopusch]

Hello everyone,

I have been having issues with neomutt for the last few days involving IMAP
connection losses on (almost?) all interactions with the mail server.

Every time I open a folder in neomutt it begins fetching the needed data
before stopping with the message "Mailbox
postmaster at jotoho.de@imap.mailbox.org geschlossen". (Translation: "Mailbox
{imap_url} closed") 

It then apparently retries connecting before letting me into the folder but
none of the mails are actually being shown. The mail selector (cursor)
oftentimes hangs in the middle of an empty list of emails.

To make the emails actually show, I then need to exit and reenter that folder
again. When scrolling through bigger folders like my mail archive the client
sometimes connects to the server again, just to fail with the same message as
on opening the folder but with no obvious effect.

Neither my secondary mail client on the same PC (evolution) nor K-9 Mail on
my smartphone show any issues working with my mail provider. I wanted to find
out which side was responsible for closing the IMAP connections so I took a
look at the connections with the provider using Wireshark. Apparently the
connections are closed due to my PC sending repeated TCP RESET packets.
These things make me believe the issue lies on neomutt's side rather than my
providers.

Curiously, the ArchLinux website says that the package was not updated since
February, so that excludes a change in neomutt from being the cause. Since my
neomutt configuration is stored in a git repository, I was also able to
confirm that recent changes in the neomuttrc file are not to blame by rolling
back to the end of July when the issue didn't exist and confirming that the
error still happened. The only thing I can think of is something like a
breaking change or regression in a dependency of neomutt that broke stuff.

Perhaps unrelated: Around the time this first happened, I had accidentally
moved a folder of my mailbox into another folder using evolution before
quickly moving them back to their normal place. This is the second time that
happened and both times this caused "phantom folders" to appear in neomutt. I
presume that they are (temporary) folders that existed while moving folders
around and do not exist anymore but are still registered somewhere. 
(Maybe in this mysterious list of "subscribed" folders on the server that's
mentioned in the neomutt documentation? Don't know how IMAP works in detail)
The phantom folders are neither shown in evolution, K-9 Mail nor the webmail
client of my provider.

Trying to open those phantom folders makes neomutt report that "IMAP command
failed: a0044 NO Mailbox doesn't exist: twitch/software" but they still
remain in the list of folders. (I'm using the option "set
imap_check_subscribed" in neomuttrc)
Since no issue like this happened the first time those phantom folders
appeared I'm thinking that maybe those four phantom folders break some
internal limit on tolerated IMAP errors that wasn't broken with only two
phantom folders? Don't know if there is any merit to that train of thought.

Please let me know if I need to provide any further information to help debug
this issue.

Thanks in advance.

-- 
Jonas Tobias Hopusch
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