Dovecot behind Load Balancer

Jean-Daniel Dupas jddupas at
Wed Jul 10 12:54:01 EEST 2019

> Le 10 juil. 2019 à 11:46, Paolo Daniele <paolo.daniele at> a écrit :
> Il 10/07/19 11:44, Jean-Daniel Dupas ha scritto:
>>> Le 10 juil. 2019 à 10:24, Paolo Daniele via dovecot <dovecot at> a écrit :
>>> Il 10/07/19 10:20, Aki Tuomi ha scritto:
>>>>> On 12/06/2019 20:02 Paolo Daniele via dovecot <dovecot at> wrote:
>>>>>  Hi,
>>>>>  i've a question for you.
>>>>>  I've two dovecot imap/pop server behind a zen load balancer.
>>>>>  Load balancing is made by lx4nat so the public ip address of my load balancer contact directly the dovecot servers.
>>>>>  Since few months i've a message from thunderbird that i've reached the imap limit login for ip.
>>>>>  I've triend to increase the max user ip parameter but sometimes i've the same problem.
>>>>>  It's a strange things that actually i'm able to mitigate by reduce the number of cached connections in Thunderbird but it's not normal.
>>>>>  What do you think about that?
>>>>>  Maybe there's some tuning that you can suggest.
>>>>>  Thank you,
>>>>>  Paolo
>>>> Have you ensured, by checking logs, that the connections are seen by dovecot to come from public IP addresses?
>>>> Also, thunderbird is known to open lots of concurrent connections.
>>>> Aki
>>> Yes,
>>> connections are coming from the ip address of load balancer (also checked with a netstat -an)
>> If connection are seen as coming from the IP address of the load balancer, isn't it normal that dovecot complains ?
>> That means that dovecot sees all connections as coming from a single client, which would explain why you reach that limit.
> Yeah of course, but i've checked that i haven't reach the max_user_per_ip limit by counting dovecot process coming from that ip address.
> So the strange and the reason why i'm writing to you :)

Don't know if this is still relevant in your dovecot version, but did you see this: <>

People had some issue by using the mail_max_userip_connections in the imap section and had to set it in the global section instead.

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