Issue Invalid argument: Undelivered Mail Returned to Sender

[Ihtshama]

I am recieveing emails from almost all senders, but one customer is not able to send emails, he is seeing following error

The mail system

<hello@domain.ch>: connect to
mail.domain.ch[95.216.40.xxx]:25: Invalid argument

Can you please advise why it is happeing?

 

[IgorG]

First, find the ip addresses of the transports used in the postfix configuration. For example:

# grep smtp_bind_address /etc/postfix/master.cf

plesk-104.248.xxx.xxx- unix - - n - - smtp -o smtp_bind_address=104.248.xxx.xxx -o smtp_bind_address6= -o smtp_address_preference=ipv4
plesk-185.98.xxx.xxx- unix - n n - - smtp -o smtp_bind_address=185.98.xxx.xxx -o smtp_bind_address6= -o smtp_address_preference=ipv4

Then check which one is used for your domain with the problem:

# postmap -s /var/spool/postfix/plesk/sdd_transport_maps | grep 104.248.xxx.xxx
# postmap -s /var/spool/postfix/plesk/sdd_transport_maps | grep 185.98.xxx.xxx

When you determine the IP address of the transport used for your problem domain, check that this IP address really exists on your Plesk server and is correctly configured in Plesk.