err="read: EOF (io error)" can't send any emails with external apps

[FutureCow]

Yesterday everything was working fine, but today I can't send any emails with outlook or snappymail (webmail). I don't know what is changed, that things stopped working. Also setting up a new account inside Microsoft Outlook isn't working. Got all the green vinkjes at the DNS test page. I'm using NPM, but everything worked yesterday. Sending mail with the build-in webmail is working.

This is what i got in de log:

Feb 27 19:05:26 mail mox[685]: l=info m="new connection" pkg=imapserver remote=[2a0d:ipv6]:58868 local=[2a0d:ipv6]:993 tls=true viahttps=false listener=public cid=19548cbe9ce delta="72.403µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="starting tls server handshake" pkg=imapserver cid=19548cbe9ce delta="559.821µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="tls handshake completed" pkg=imapserver version=tls-1.3 ciphersuite=TLS_AES_128_GCM_SHA256 sni=mail.mydomain.nl resumed=false clientcerts=0 cid=19548cbe9ce delta=1.681151ms
Feb 27 19:05:26 mail mox[685]: l=debug m="scram auth" pkg=imapserver authentication=info@mydomain.nl cid=19548cbe9ce delta=1.135121ms
Feb 27 19:05:26 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=authenticate duration=289.348287ms cid=19548cbe9ce delta=289.356419ms username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=enable duration="94.297µs" cid=19548cbe9ce delta=1.351387ms username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=info m="new connection" pkg=smtpserver remote=[2a0d:ipv6]:39272 local=[2a0d:ipv6]:465 submission=true tls=true viahttps=false listener=public cid=19548cbe9cf delta="215.644µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="starting tls server handshake" pkg=smtpserver cid=19548cbe9cf delta="59.835µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="tls handshake completed" pkg=smtpserver version=tls-1.3 ciphersuite=TLS_AES_128_GCM_SHA256 sni=mail.mydomain.nl resumed=false clientcerts=0 cid=19548cbe9cf delta=2.231879ms
Feb 27 19:05:26 mail mox[685]: l=debug m="smtp command result" pkg=smtpserver kind=submission cmd=ehlo code=250 ecode= duration="46.263µs" cid=19548cbe9cf delta="452.922µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="scram auth" pkg=smtpserver authentication=info@mydomain.nl cid=19548cbe9cf delta="622.285µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="smtp command result" pkg=smtpserver kind=submission cmd=auth code=235 ecode=2.7.0 duration=8.078217ms cid=19548cbe9cf delta=7.692567ms username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=info m="connection closed" err="read: EOF (io error)" pkg=smtpserver cid=19548cbe9cf delta="867.379µs" username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=logout duration="28.07µs" cid=19548cbe9ce delta=27.892044ms username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=info m="connection closed" pkg=imapserver cid=19548cbe9ce delta="93.922µs" username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=info m="new connection" pkg=imapserver remote=[2a0d:ipv6]:58880 local=[2a0d:ipv6]:993 tls=true viahttps=false listener=public cid=19548cbe9d0 delta="43.042µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="starting tls server handshake" pkg=imapserver cid=19548cbe9d0 delta="26.742µs"
Feb 27 19:05:26 mail mox[685]: l=debug m="tls handshake completed" pkg=imapserver version=tls-1.3 ciphersuite=TLS_AES_128_GCM_SHA256 sni=mail.mydomain.nl resumed=false clientcerts=0 cid=19548cbe9d0 delta=1.625724ms
Feb 27 19:05:26 mail mox[685]: l=debug m="scram auth" pkg=imapserver authentication=info@mydomain.nl cid=19548cbe9d0 delta="983.392µs"
Feb 27 19:05:26 mail mox[685]: l=info m="login attempt" pkg=smtpserver address=info@mydomain.nl account=info protocol=submission authmech=scram-sha-256 result=ok remoteip=2a0d:ipv6:9f9d localip=2a0d:ipv6:c238 tls="version=tls1.3 ciphersuite=tls_aes_128_gcm_sha256 sni=mail.mydomain.nl resumed=false alpn=" useragent= tlspubkeyfp= count=1 cid=19548cbe9cf username=info@mydomain.nl
Feb 27 19:05:26 mail mox[685]: l=info m="login attempt" pkg=imapserver address=info@mydomain.nl account=info protocol=imap authmech=scram-sha-256 result=ok remoteip=2a0d:ipv6:9f9d localip=2a0d:ipv6:c238 tls="version=tls1.3 ciphersuite=tls_aes_128_gcm_sha256 sni=mail.mydomain.nl resumed=false alpn=" useragent= tlspubkeyfp= count=6 cid=19548cbe9ce username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=authenticate duration=387.202391ms cid=19548cbe9d0 delta=387.220725ms username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=enable duration="103.672µs" cid=19548cbe9d0 delta="709.981µs" username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=status duration="185.437µs" cid=19548cbe9d0 delta=3.099435ms username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=select duration=1.069212ms cid=19548cbe9d0 delta=2.020512ms username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=debug m="imap command done" pkg=imapserver cmd=logout duration="86.965µs" cid=19548cbe9d0 delta=1.623162ms username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=info m="connection closed" pkg=imapserver cid=19548cbe9d0 delta=1.967219ms username=info@mydomain.nl
Feb 27 19:05:27 mail mox[685]: l=info m="login attempt" pkg=imapserver address=info@mydomain.nl account=info protocol=imap authmech=scram-sha-256 result=ok remoteip=2a0d:ipv6:9f9d localip=2a0d:ipv6:c238 tls="version=tls1.3 ciphersuite=tls_aes_128_gcm_sha256 sni=mail.mydomain.nl resumed=false alpn=" useragent= tlspubkeyfp= count=7 cid=19548cbe9d0 username=info@mydomain.nl

What can i do to debug this more?

[mjl-]

Thanks for reporting!
From the messages about the login attempts, this looks like a recent post-v0.0.14 version. Did submission stop working right after updating from v0.0.14? Or was there an update to the mail client? (Multiple clients show the behaviour, right? So it's more likely a change in mox). Is this logging from snappymail btw? Or another client?
The logging shows that the authentication did succeed. For IMAP, the connection proceeds with some commands (the last part of the logging). For submission (SMTP) the client closes the connection after successful authentication. The cid fields are connection ids in case that wasn't clear.
I think a next step is enabling trace-level logging and seeing the messages being exchanged. You can also do level "traceauth" for potentially even more details (sensitive details!). There is a risk that the client decides to abort the connection. That wouldn't leave any hint in the tracing output. But perhaps there is logging in the mail client about the decisions.
You can also do local testing relatively easily with "mox localserve", it prints instructions.

I'm using NPM, but everything worked yesterday.

Don't know if this is important, but I don't think I understand what you mean by this. (:

[FutureCow]

Didn't received a messages from GitHub that you responded to the issue.
After removing all my accounts from Outlook and add them back again, the problems with outlook seems gone. I will test this further today. So only the problem with snappymail is left, but it seems the problem is from snappymail:
the-djmaze/snappymail#1813

with also a fix, but not released yet:
the-djmaze/snappymail@64e780e

So will try to fix this myself!