mailing USA tax forms - how?

[itsme]

Hi all,

just a quick question. if you are mailing more than 1 years tax return, are you supposed to mail them separately or together? if i forgot 2008 and want to mail it and 2009 return now, can i send them all in the same envelope to the IRS? I know it's a strange question but someone on another forum said to make sure they are mailed separately...

thanks!