Sentora and 1and1: trouble with DNS MX records

[Broken5entora]

I have a server with Sentora installed on CentOS 6 and a domain (let's say mydomain.com) bought from 1and1. 

Here are the settings I made in 1and1 web interface:

    Name Server Settings 
    Name servers: 
    (*) 1&1 name servers
    ( ) Other name servers
    
    A/AAAA and CNAME Records 
    IP address (A Record):
    ( ) 1&1 IP address
    (*) Other IP address
    IPv4 Address 111.222.33.44
    IPv6 Address (empty)
    
    MX Records 
    Mail Exchanger (MX Record):
    ( ) 1&1 mail server
    (*) Other mail server
    MX1  mail.mydomain.com Priority 10
    MX2 
    MX3 
    MX4 
    
    TXT and SRV Records 
    (none)

In Sentora I made a mailbox me@mydomain.com
I sent an email from my other mailbox me@gmail.com to me@mydomain.com, it did not arrive nor I received an error response from the server.
And the other way round, mails from me@mydomain.com to me@gmail.com are silently dropped too. 

Also while I can see target mail.mydomain.com in Domain Management / DNS Manager I cannot resolve mail.mydomain.com.

What did I do wrong and how to fix it?