# Cannot send email - problem with TLS

**URL:** <https://meta.discourse.org/t/cannot-send-email-problem-with-tls/330606>\
**Category:** Self-hosting\
**Tags:** email\
**Created:** [October 12, 2024, 6:56pm UTC](https://meta.discourse.org/t/cannot-send-email-problem-with-tls/330606 "2024-10-12T18:56:58Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![laplasz](https://sea3.discourse-cdn.com/meta/user_avatar/meta.discourse.org/laplasz/32/221485_2.png) [@laplasz](https://meta.discourse.org/u/laplasz)\
**Post date:** [October 12, 2024, 7:00pm UTC](https://meta.discourse.org/t/cannot-send-email-problem-with-tls/330606/2 "2024-10-12T19:00:47Z")

</div>

The problem was with the mtu size of docker interface. I have a PPPoE connection which has less then 1500 bytes mtu size - so what I had to do is to set MSS clamping in iptables.

```plaintext
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

```

More info about the solution can be found here: [https://stackoverflow.com/a/79081640/1342413](https://stackoverflow.com/a/79081640/1342413)

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