Q: when I switch to iCloud, will I lose keychain?

Hello, nope, but Keychain is where your passwords are stored, no real relation to Mail other than it can store your Mail passwoed(s).

Don't delete you old MM account yet, do this...

I think they're slowly nudging people to switch, .mac & MobileMe are going away about July, may as well set it up now.

I understand .mac & MobileMe mail will still come through.

iCloud Mail setup, do not choose .mac or MobileMe as type, but choose IMAP...

IMAP (Incoming Mail Server) information:

▪ Server name: imap.mail.me.com

▪ SSL Required: Yes

▪ Port: 993

▪ Username: example@me.com (use your @me.com address from your iCloud account)

▪ Password: Your iCloud password

SMTP (outgoing mail server) information:

▪ Server name: smtp.mail.me.com

▪ SSL Required: Yes

▪ Port: 587

▪ SMTP Authentication Required: Yes

▪ Username: example@me.com (use your @me.com address from your iCloud account)

▪ Password: Your iCloud password