Non-user logins?

[N]

As Dave mentioned, Fail2ban.

You'll likely want to set up graduated responses with fail2ban so the 
more they try, the longer it takes for them to get off the ban list.

Best

N


On 1/7/22 20:35, Ken Wright wrote:
> On Fri, 2022-01-07 at 23:27 -0500, Dave McGuire wrote:
>> On 1/7/22 11:24 PM, Ken Wright wrote:
>>> My Dovecot issues continue.  Right now I see at least two issues:
>>> first, my logs consistently show non-users trying (and failing) to
>>> log in, and I'm still unable to log in from my email client
>>> (Evolution or Roundcube, either one).
>>>
>>> I'll post about the second issue later; right now I wonder why I'm
>>> getting so many non-users trying to log in.  Am I the subject of
>>> concerted hacking attacks, or is there something else going on?
>>> Some of the attempted logins are more-or-less random names claiming
>>> to be @mydomain, but at least one is a username that's really on my
>>> server, to wit:
>>>
>>> Jan  7 22:52:01 grace dovecot: lmtp(776281): Error: lmtp-server:
>>> conn unix:pid=776262,uid=117 [3]: rcpt www-data at mydomain.com:
>>> Failed to lookup user www-data at mydomain.com: Internal error
>>> occurred. Refer to server log for more information.
>>>
>>> (Another quick question:  which server log should I check?)
>>>
>>> So, if anyone can tell me what's going on with all these logins,
>>> I'd be much obliged!
>>     I see them all the time on the mail servers I run.  Typical kids
>> trying to mess with other peoples' stuff.  I run fail2ban to catch
>> those log entries and block the source IP address for a month on the
>> first failed login.  At any one time I have between 12,000 and 15,000
>> addresses in my blocked list for IMAP.
> Dave, that's exactly the kind of answer I was looking for.  Fail2ban,
> huh?  I'll have to check that out.  Thanks again!
>
> Ken
>