The mailing instructions should have been included when you printed your forms.
If not, please click on the link below.
The mailing address is dependent on where you live, what form you are filing, and if you are including a tax payment or expecting a refund.
The only requirement, as far as envelopes, would be restricted by the United States Postal Service, not the IRS.
MAILING
ADDRESSES for Federal Tax Returns, please click here.