[CentOS] Partition advice

I'm setting up a new mail server (dovecot + sendmail + SpamAssassin + 
ClamAV + MIMEDefang) to replace an aging CentOS 6 box. The new box is a 
low-end PowerEdge with an SSD, 3 4TB red drives on a PERC RAID controller 
which I'll probably set up RAID5, and possibly mirrored internal SD cards 
as a boot device. I'm debating how to partition it and am soliciting advice.

My initial instinct is to put /boot and the OS on the SSD and the home 
directories with their mail store on the RAID array. I might put a rescue 
partition on the internal SD drive (which is normally intended for a VM 
host). Does anyone see anything wrong with that? Should I do something 
different? Anything I should avoid putting on the SSD, such as swap, /tmp, 
and /var/tmp?

I've been running Red Hat as a small office server since 5.2 back in the 
90's. I'm trying to create a system that's easy to fix when it breaks. I 
find that's the real power of Linux over any other OS: It's easy to fix 
when it breaks.

Oh, and backup will be to an external USB drive using BackupPC, with the 
drive regularly swapped off-site, plus an off-site rsync mirror.