Hello,
I have a fairly new installation of the Dovecot server version 2.3.19.1 on Debian 12.8.
In general, the server works correctly. It sends and receives emails without issues. The clients primarily use Thunderbird on desktops and Gmail on Android.
However, some clients are using iPhones with various hardware versions. Those with iOS below version 18 work correctly without any issues. Those who have updated their phones to version 18 and now even 18.2 are experiencing problems with mailbox synchronization.
On version 18.2, the issue appears as follows: When you open the app, you can read several messages. They load correctly, but, for instance, attachments do not. If I wait for some time, the attachment eventually loads. During this time, I observe the server logs, and it shows that a certain session on the Dovecot server has ended.
Dec 17 13:13:01 iredmail0 dovecot[408]: imap(xxx@xxx.com)<44785><1QGZCHcp/+3AqM2O>: Disconnected: Connection closed (UID SEARCH finished 92.295 secs ago) in=2972 out=6076956 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=36 body_bytes=6059064
Dec 18 08:40:41 iredmail0 dovecot[408]: imap(xxx@xxx.com)<177412>: Disconnected: Connection closed (UID FETCH finished 90.079 secs ago) in=5126 out=1304237 deleted=0 expunged=0 trashed=0 hdr_count=94 hdr_bytes=289688 body_count=89 body_bytes=969615
Dec 18 08:42:19 iredmail0 dovecot[408]: imap(xxx@xxx.com)<177410><D5mqU4cpZ+nAqM2O>: Disconnected: Connection closed (UID FETCH finished 95.051 secs ago) in=4475 out=1162785 deleted=0 expunged=0 trashed=0 hdr_count=95 hdr_bytes=281674 body_count=61 body_bytes=839545
Dec 18 08:44:17 iredmail0 dovecot[408]: imap(edyta.kowalewska@laktopol.com.pl)<177918>: Disconnected: Connection closed (UID FETCH finished 92.132 secs ago) in=29399 out=30266644 deleted=0 expunged=0 trashed=0 hdr_count=565 hdr_bytes=1726228 body_count=628 body_bytes=28109455 After the session is closed, the attachment loads immediately. From the logs and router analysis, it appears that the download happens in another previously opened session.
After this incident, I go to another message with an attachment, and the situation repeats. There are also situations where the email body does not load, and the app waits for the server until the session closes and the content is fetched in another session.
It does not matter whether I connect to the server via the internet or through a local network.
On an iPhone 7 with iOS 15.8.3, everything works smoothly. Attachments open without issues.
On iOS 18.1.1, attachments do not load, and the session does not close on its own. It takes forever unless the app is closed.
In the Gmail app, everything works correctly without any issues.
This is clearly a problem with the mail client on iPhone. However, is there anything I can adjust in my server settings to mitigate this issue for users?
My dovecot configuration https://pastebin.com/UPNQ5dZz