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Issue STMP QUIT / Disconnect Problem with TLS

SimonB

New Pleskian
Server operating system version
Windows Server 2019
Plesk version and microupdate number
18.0.48
Hi


We recently updated to Plesk v18.0.48 and with it MailEnable Standard v10.42

After the update we are experiencing some problem using SMTP with TLS (port 587), it appears the QUIT command no longer causes the server to disconnect the STMP connection.

We have Plesk running on an Azure VM (Windows Server 2019) so use MailEnable to send emails to SendGrid for distribution.

If we send emails from our email client to our webserver using SMTP Port 587 with Explicit TLS, the email sends fine, but when the email client sends the QUIT command the server responds `221 Service closing TLS SSL transmission session` but the server does not close the session.

If we turn off Explicit TLS and swap to port 25, the response from the QUIT command is `221 Service closing transmission channel` and the server closes the session.

We have tried downgrading MailEnable to an older version, but the problem persisted, we also tried updating it to v10.43 with no luck.

The mail client we are using hasn't been updated

Has anyone experienced this or have any idea what we could check / test to try and fix this problem?

Ideally we don't want to tell all out customers to turn off TLS

Here is the end of the STMP logs, in case that help

TLS enabled
> . < 250 Requested mail action okay, completed > QUIT < 221 Service closing TLS SSL transmission session

TLS not enabled
> . < 250 Requested mail action okay, completed > QUIT < 221 Service closing transmission channel
 
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