Yes, use IRS Form 8453 and mail it in within 3 days of e-file.

But before you mail it, ask yourself if it is really needed.  Folks tend to try to attach a lot of extra crap that the IRS ignores anyway.

Thanks.  Familiar with that form but it restricts the type of attachment.   I have a Section 266 election.  I guess it does not hurt to ahead and submit with Form 8453 and see what happens- if anything I have a record of it.  Have you use for attachments not listed on the form?