I don't know much about the internals of PM, but it seems like your MX host is not accepting mail (at least not from my machine).

$ host -t mx lums.edu.pk
lums.edu.pk             MX    50 abaseen.lums.edu.pk

$ host abaseen.lums.edu.pk     
abaseen.lums.edu.pk     A       172.28.1.2
abaseen.lums.edu.pk     A       203.128.0.2

$ telnet  203.128.0.2 smtp
Trying 203.128.0.2...
Connected to 203.128.0.2.
Escape character is '^]'.
Connection closed by foreign host.
[download]

The other host (172.28.1.2) seems to time out on me.