MTN's mail server inaccessible on their own 3G network

[Shadowfax]

I don't know if you've noticed this, but with repeating regularity the hosts mail.mtn.co.za and smtp.mtn.co.za are not reachable from MTN's own 3G network. No problems with any other sites, it appears, and I can ping both of these servers from outside MTN's 3G network.

To say that this is annoying is an understatement. I can't send mail, and am forced to paste stuff into a fallback gmail a/c to get it out.

Trying to find someone to complain to at MTN is futile - doubly so while they are striking.

Any advice?