Email On A "Macintoh SE/30"

yes it's possible but before someone gives detailed instructions, it'd be nice to know how your SE/30 is setup
How much RAM
What version of MAC OS
Does it have an ethernet card
Do you already have a dialup or high speed internet

http://www.jagshouse.com/classicinternet.html has a good guide on getting it on the web and using e-mail, internet, telnet etc. The package includes Eudora, probably the best e-mail client for classic macs. It's on Floppy disk images, but you could probably mount them on the desktop using Disk Copy.