mrichter@CL-LINUX-3OG-MR:~$ telnet mxzhh.bluewin.ch 25
Trying 195.186.227.50...
Connected to mxzhh.bluewin.ch.
Escape character is '^]'.
421 4.4.5 Service unavailable, concurrency limit reached.
Connection closed by foreign host.

Trying 195.186.227.50...
telnet: connect to address 195.186.227.50: Connection refused
telnet: Unable to connect to remote host


This with all 3 MX:

bluewin.ch.        88    IN    MX    10 mxbw.bluewin.ch.
bluewin.ch.        88    IN    MX    42 mxzhb.bluewin.ch.
bluewin.ch.        88    IN    MX    42 mxzhh.bluewin.ch.