I am just passing on, with permission, something exim related
from the mailop@??? list.
https://list.mailop.org/private/mailop/2021-December/020647.html
On 02/12/2021 12:50, Andrew Hearn via mailop wrote:
> Hello,
>
> We're a UK ISP, and relay email for our customers as well as send our
> customers emails such as invoices.
>
> We currently have about 1,000 emails queued for google accounts and
> these are failing with a timeout, eg from exim:
>
> 2021-12-02 11:48:05 1msize-005feQ-DI H=gmail-smtp-in.l.google.com
> [142.250.13.26] TLS error on connection (send): The TLS connection was
> non-properly terminated.
>
> 2021-12-02 11:48:05 1msize-005feQ-DI H=gmail-smtp-in.l.google.com
> [142.250.13.26]: SMTP timeout after sending data block (525043 bytes
> written): Connection timed out
>
> Based on past experience, eventually, the emails may will through.
>
> This is also intermittent, as sending to my own gmail address tends to
> get through eventually, though they do still time out once or twice
> before eventually getting through.
>
> Generally these emails do show as SPF/DKIM/DMARC PASS in gmail.
>
> This report is rather vague, but we do have further examples, logs,
> pcaps.
>
> Is someone from google on this list able to help investigate this
> problem with us please? I can pass examples and pcaps privately.
>
> Thanks!
>
> Andrew, AS20712 aa.net.uk
In
https://list.mailop.org/private/mailop/2021-December/020659.html
he followed up:
> After trying a few things, disabling TCP Fast Open seems to have worked...
>
> My mail queue is being delivered successfully to Google MXs!
>
> A bit more about our system:
> Stock Exim from Debian 11, using GnuTLS.
> Exim version 4.94.2 #2 built 13-Jul-2021 16:04:57
>
> And I added:
> hosts_try_fastopen =
> to the outbound smtp transport.
>
> Andrew.
