Issue Switched Server from Plesk 17.8.11 to 18.0.21

[Puma7]

Hi,

I have a big issue but I have no clue where I should start to investigate this issue :/

What happened:
I decided to use a new Server from Hetzner with Plesk Obsedian and which from my old Server with Plesk Onyx (always the latest version). Both a running on Ubuntu 18.04.3 LTS‬ with similar hardware.
I used the "Migration & Transfer Manager" to transfer data and databases to the new server. Everything is running and seams to be fine. But i noticed the the two Shopware Shops which I transferred act weird if I want to send E-Mails.
The only log that I could find was:

{"exception":"[object] (Zend_Mail_Protocol_Exception(code: 0): Connection timed out at /var/www/vhosts/shop.com/httpdocs/ShopDir/engine/Library/Zend/Mail/Protocol/Abstract.php:273)"} {"uid":"ad5d213"}

Now I thought it would be an issue with the Firewall (Hardware and/or Software) or the SMTP Server blocks the IP of the Server. But I con't find any issues.

Has anyone a idea what else could lead to an connection time out?
Maybe some permissions are not correct?

P.S.
The SMTP Server is smtp.office365.com with tls on port 587

 

[Puma7]

Ok, I know now the reason ... it's IPv6
But I have absolutely no clue why. Maybe and Ubuntu kernel issue?

What happens:
After I restart the Server all connections work fine. "ping6 google.com" works great
After 10-30 minutes "ping6 google.com" doesn't work any more. No logs, no clue.
Also mails don't work because the server tries to send them over ipv6 but cant connect to the destination. But DHCP6 seam to work. The Server knows the destination ipv6 address but simply can't get the information through.

I'm really confused what cloud cause such an issue on a fresh Ubuntu+Plesk+Hetzner constellation. I would be really happy about further ideas how to solve such an issue.

I hotfixed the problem by deactivating the ipv6 with:
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1

 

[Ales]

Can you connect to the above SMTP from the new server's shell? Try:

openssl s_client -starttls smtp -showcerts -connect smtp.office365.com:587

EDIT: Please disregard, I just saw your second post. I don't have any experience with Hetzner, perhaps another forum member will be able to help. Their support should also be aware of any similar IPv6 issues...