Hi Wietse,

That fixed it.

Thank you for helping me out. It was a custom written content filter built
with python. The python modules defaulted to 32M size.

On Mon, Sep 8, 2025 at 10:08 PM Wietse Venema via Postfix-users <
[email protected]> wrote:

> Kladizkov theone via Postfix-users:
> > Hello there,
> >
> > I?m running Postfix and have configured a custom content filter on
> > localhost ( a python service that listens at 10025 ). When sending large
> > messages, Postfix rejects them with the following error:
> >
> > message size 34639078 exceeds size limit 33554432 of server
> localhost[127.0.0.1]
>
> The SMTP-based content filter server announces a SIZE limit of 33554432.
> If that is not the limit that you need. change the content filter.
>
> Assuming this is the setup:
>
> upstream Postfix SMTP client -> content filter -> donwstream Postfix SMTP
> serer
>
> You can test this by hand with
>
>     telnet localhost port-of-content-filter
>
>     ehlo localhost
>
> The filter will announce SIZE=33554432
>
> Some content filters will announce the SIZE limit from the down-stream
> Postfix SMTP server. In that case, you need to change the settings
> there.
>
> You can test this by hand with
>
>     telnet localhost  port-of-downstream-smtp-server
>
>      ehlo localhost
>
> And verify that this announces the SIZE= value that
> you expect Postfix to use.
>
>         Wietse
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