Send mail with differenet ip adresses

That's possible, but not in ISPConfig directly, you'll have to do this in postfix.

add this line in main.cf:

sender_dependent_default_transport_maps = hash:/etc/postfix/sdd_transport

Then create a file:

/etc/postfix/sdd_transport

which contains lines like this:

@domain1.tld othersmtp:
@domain2.tld othersmtp:

and then you have to add a smtp2 stanza in postfix master.cf file (somewhere at the beginning after the 'smtp' line. Example:

Code:

othersmtp     unix -       -       n       -       -       smtp
    -o smtp_bind_address=1.2.3.4
    -o smtp_helo_name=mx2.yourdomain.tld[code]

Probably you find a more sophisticated guide on the topic when you search for sender_dependent_default_transport_maps though :)