ot: how to t/s TBird problems ?

[Voytek Eymont]

I have a Dovecot/Postfix/MariaDB on a Centos, just have a user ask me:

------------------
I recently upgraded my Thunderbird email client and have experienced
problems since.
It appears that when Tbird polls for new messages it gets held up
waiting for a response from the server
I'm using POP port 995.
Any ideas as to why I'm having a problem ?
-------------------

how to investigate such issue ?

CentOS release 6.10 (Final)
# dovecot --version
2.3.11.3 (502c39af9)
load average on server 0.05/0.01
user log shows like:


Oct 12 10:08:50 pop3-login: Info: Login: user=<user at tld.com.au>,
method=PLAIN, rip=49.111.222.333, lip=103.xxx.yyy.zzz, mpid=17371, TLS,
session=<E83xW8rqDPkxw3EW>
Oct 12 10:09:34 pop3(user at tld.com.au)<17371><E83xW8rqDPkxw3EW>: Info:
Disconnected: Logged out top=0/0, retr=0/0, del=0/114194, size=10616009472
Oct 12 10:14:36 imap-login: Info: Login: user=<user at tld.com.au>,
method=PLAIN, rip=49.111.222.333, lip=103.xxx.yyy.zzz, mpid=17460, TLS,
session=<ftiLcMrqR/gxw3EW>
Oct 12 10:14:37 imap(user at tld.com.au)<17460><ftiLcMrqR/gxw3EW>: Info:
Logged out in=152 out=69724 deleted=0 expunged=0 trashed=0 hdr_count=0
hdr_bytes=0 body_count=1 body_bytes=68628
Oct 12 10:28:27 pop3-login: Info: Login: user=<user at tld.com.au>,
method=PLAIN, rip=49.111.222.333, lip=103.xxx.yyy.zzz, mpid=17714, TLS,
session=<+WsXosrqK/gxw3EW>
Oct 12 10:29:16 pop3(user at tld.com.au)<17714><+WsXosrqK/gxw3EW>: Info:
Disconnected: Logged out top=0/0, retr=1/76174, del=0/114195,
size=10616085600
Oct 12 10:32:19 imap-login: Info: Login: user=<user at tld.com.au>,
method=PLAIN, rip=49.111.222.333, lip=103.xxx.yyy.zzz, mpid=17817, TLS,
session=<bZftr8rqq/gxw3EW>
Oct 12 10:32:20 imap(user at tld.com.au)<17817><bZftr8rqq/gxw3EW>: Info:
Logged out in=153 out=135592 deleted=0 expunged=0 trashed=0 hdr_count=0
hdr_bytes=0 body_count=1 body_bytes=134503
Oct 12 10:45:58 imap-login: Info: Login: user=<user at tld.com.au>,
method=PLAIN, rip=49.111.222.333, lip=103.xxx.yyy.zzz, mpid=18081, TLS,
session=<U3674Mrqzfgxw3EW>
Oct 12 10:45:59 imap(user at tld.com.au)<18081><U3674Mrqzfgxw3EW>: Info:
Logged out in=152 out=24602 deleted=0 expunged=0 trashed=0 hdr_count=0
hdr_bytes=0 body_count=1 body_bytes=23514
Oct 12 10:48:49 pop3-login: Info: Login: user=<user at tld.com.au>,
method=PLAIN, rip=49.111.222.333, lip=103.xxx.yyy.zzz, mpid=18135, TLS,
session=<y1/r6srqtPsxw3EW>
Oct 12 10:49:53 pop3(user at tld.com.au)<18135><y1/r6srqtPsxw3EW>: Info:
Disconnected: Logged out top=0/0, retr=2/166190, del=0/114197,
size=10616251743
Oct 12 10:50:42 imap(user at tld.com.au)<3274><cr10yqTqifgxw3EW>: Info:
Logged out in=192516 out=5957294 deleted=0 expunged=0 trashed=0
hdr_count=263 hdr_bytes=358656 body_count=126 body_bytes=5110403
Oct 12 10:50:42 imap(user at tld.com.au)<3271><hLl0yqTqh/gxw3EW>: Info:
Logged out in=78324 out=58677 deleted=0 expunged=0 trashed=0 hdr_count=0
hdr_bytes=0 body_count=0 body_bytes=0

Voytek