A user reported that she was unable to get her email today and was receiving
an error in Outlook when she attempted to download her email. I logged into
the email server, which runs
Dovecot. I tried
establishing a telnet connection to the
POP3 port on
the server. I was able to successfully connect to the
well-known port,
TCP
port 110, used for POP3 connections. I could then enter the user's
username with the user command, but I never received a
reponse from the server, i.e. from Dovecot. I eventually had to hit
ctrl-], i.e., the Ctrl and "]" keys to return to the shell prompt.
$ telnet 127.0.0.1 110 Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. user nell ^] telnet> quit Connection closed. $
I've encountered the same issue in the past, but haven't been able to track down the cause yet. E.g., see Dovecot not responding. As I've done previously, I checked on entries in today's and yesterday's mail logs for any entries that might be related to the problem and for the number of dovecot processes running. I saw a lot of dovecot process entries; 59 of those entries were pop3-login ones.
# egrep -c -i dovecot.*(error|warning) /var/log/maillog 0 # grep -i dovecot /var/log/maillog # grep -i dovecot /var/log/maillog.1 # grep -i pop3 /var/log/maillog # grep -i pop3 /var/log/maillog.1 # ps -aux | grep dovecot | grep -v grep | wc -l 63 # ps -aux | grep pop3-login | grep -v grep | wc -l 59 # grep -c timeout /var/log/maillog 0 # doveadm who username # proto (pids) (ips) #
The doveadm who command didn't show any current users checking email.
I checked on whether the problem was also affecting users' ability to check email via the Internet Message Access Protocol (IMAP) - see Entering IMAP commands using Telnet - and found that I could access the mailbox of the user having a problem accessing email by POP3 with IMAP.
After checking on whether connectivity via IMAP was working, I checked the number of pop3-login entries in today's mail log file again. I saw the number had jumped from 59 to 73; I suspect now that those entries accumulate as user's attempt to download email via POP3, but are unsuccessful.
# ps -aux | grep pop3-login | grep -c -v grep 73 #
As I've done previously, I restarted the dovecot service at this point, so that users who use POP3 for their email will be able to download their email.
# service dovecot restart Redirecting to /bin/systemctl restart dovecot.service #
As before, once I restarted Dovecot, I could enter both the user's account id and password and enter other POP3 commands.
$ telnet 127.0.0.1 110 Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. +OK Dovecot ready. user nell +OK pass ASecretPassword +OK Logged in. stat +OK 234 19888118 quit +OK Logging out. Connection closed by foreign host. $
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