[xubuntu] Why does mdadm want postfix?

I'm running Xubuntu 13.04, it's been running for awhile.

I just installed a couple disks I want to set up as RAID, which by itself is no big deal to me, I've done it before.

I tried with apt-get and synaptic both, mdadm wants postfix. I installed both, and then was able to completely remove postfix with evidently no issues.

Is this in the repository or is it yet another sign that my package manager is messed up? I've been having issues.