18 November 2010
I had sent 3 ITR-V in one envelope and all of them have been acknowledged to be received by IT Department by email. So there is no restriction as such.
22 June 2011
i have been sending 10-12 ITR's in one envelop.. so nothing specific in this regard, but should not be more than 20 so that if the mail misses, you doesn't loose much