Resolved E-mail works, connection trough apps(Outlook, Spark, Gmail etc) not

[Weerz]

Server operating system version

Ubuntu 18.04.6 LTS

Plesk version and microupdate number

Plesk Obsidian Version 18.0.48

Hi,

Have an issue that I can't figure out.
Own Plesk VPS at strato, e-mail works and I can log in via webmail or native e-mail on iPhone/iPad.

Server is fully up to date and plesk obsidian 18.0.48 as well.
Devcot/postfix runs on it.

But now I wanted to use a slightly more advanced app through Outlook, Spark, Gmail.
The only problem is here, I can't connect.
Is on multiple devices where it doesn't work with setup.
Imap, enter data then get to see that no connection can be made.

Setting up native e-mail on iPhone/iPad/Mac does work, including deleting account and setting up again. Webmail also fine.

Checked settings from native and used the ports (993,587,465) that work natively as ports on the apps.
No success.

Working e-mail:
- Webmail
- Native e-mail client iOS/Mac OS

Not connecting on multiple devices to different domain accounts:
- Outlook
- Gmail
- Spark

Checked everything on the server, but am a bit out of my options as to where it could be.
Searching for this problem unfortunately does not yield any options that work.

Hopefully someone has some tips on where else I can look.

Thanks in advance!

 

[Kaspar]

Any error messages when you try to connect to email accounts when using those apps?

 

[Weerz]

Yes,

In Spark it just goes back in can't connect and advices to change the advanced settings.
Gmail say's it can't connect.

Outlook

 

[Maarten.]

Can you show us the settings you use in the mail clients?

Did you check the maillog for errors or other warnings?
# tail -f /var/log/mail.log

Or use the Log Browser extension to view the log file.

 

[Weerz]

strange thing is that I get it also on the native mail now when I add a new account on it.
It does show the e-mail, bit get an error about the SSL not trusted.
SSL I renewed just in case, as when I show the details it shows valid until Feb/2023.

On iPhone I don't get the errors, but the accounts on that device where already there.

Error in de mail.log from account I just added.
SSL_accept() failed: error:14094416:SSL routines:ssl3_read_bytes:sslv3 alert certificate unknown: SSL alert number 46

Accounts on the iPhone deliver no error in the mail.log and are ok.

Plesk is on TLS 1.2
TLS/cipher is on Intermediate.

 

[Maarten.]

Does the subscription have an SSL certificate assigned to the mail service?

Subscription -> Mail Settings -> SSL/TLS certificate for mail -> Lets Encrypt domain.com

Is this the same certificate you use on the Incoming Mailserver setting on the devices? Some clients want you to use a hostname like mail.domain.com for the Incoming Mailserver. That would lead to a certificate warning. Plesk uses domain.com as Incoming mailserver by default.

 

[Weerz]

Hi Maarten,

With further debugging I came across this also and that was the solution for this issue indeed.
I was expecting that I could use own domain names instead of the server one. But as it seems not ;-)
The earlier issue had nothing to do with this as I used the server domain in testing.

The issue with clients is also working now.
When I changed the TLS to modern and then back again to intermediate it somehow works now. Good off course but what I don't understand is why the modern is not working with clients. Is that because TLS 1.2 and TLS 1.3 is not available?

And many thanks for help!

 

[Maarten.]

Good to hear you've solved the issue.

The modern TLS configurations, as used in Plesk, have no fallback if the client doesn't support TLS 1.3. Therefore, Mozilla and Plesk recommend using the Intermediate configuration, which supports both TLS 1.3 and TLS 1.2.

The article below might be an interesting read for you. It explains the details of the modern, intermediate, and old presets offered by Mozilla:

Security/Server Side TLS - MozillaWiki

wiki.mozilla.org