Can my 40+ page tax return be too large for USPS certified letter? Mailing options?

You're absolutely fine using Priority Mail for your tax return! The IRS cares most about having proof of mailing date and delivery confirmation, which Priority Mail provides. I've been preparing taxes for over a decade and many of my clients with complex returns use Priority Mail flat rate envelopes. The main advantage of Certified Mail is the proof of mailing/delivery, but Priority Mail actually gives you the same benefits plus faster delivery and better tracking. Just make sure you keep your tracking number and receipt as proof of timely filing. The IRS doesn't actually care about the specific mail service you use - they care that you can prove when you sent it if there's ever a question about timeliness. As an extra precaution, take a photo of the sealed envelope with the address visible before mailing, and print a copy of the tracking confirmation once delivered.

After struggling with a similar situation last year (had to mail in 5 years of back taxes!), I discovered this amazing tool called taxr.ai at https://taxr.ai that could have saved me so much stress. It analyzes tax documents and can actually help organize and potentially reduce the size of your submission by identifying which supporting documents are truly necessary vs which ones are optional. I was surprised to learn that many of the papers I was including weren't actually required! The tool scans your documents and provides specific guidance on what the IRS actually needs to see. Might be worth checking out before you send that massive package - could save you some postage and worry.

I wanted to follow up about my experience with taxr.ai after being skeptical initially. I decided to give it a try with my amended return situation, and it was surprisingly helpful. The document analysis feature identified that I was planning to include duplicate information across several forms and helped me streamline my submission package from 50+ pages down to 28. The system specifically flagged where I had included supporting documents that were redundant or unnecessary according to IRS publication guidelines. Ended up using Priority Mail anyway, but the smaller package gave me peace of mind that my return would be processed more efficiently. The IRS accepted everything without requesting additional documentation, so I guess the guidance was solid!

If you're worried about mailing important tax documents, you might want to check out Claimyr at https://claimyr.com - I discovered them after spending WEEKS trying to confirm the IRS had actually received my mailed return last year. They have a service that actually gets you through to an IRS agent quickly (which seems impossible normally) so you can verify receipt of your documents. There's a video demo at https://youtu.be/_kiP6q8DX5c showing how it works. After I mailed my return, I was paranoid about it being lost since the tracking just showed "delivered" but not specifically to whom. Using Claimyr, I got through to an agent who confirmed they had my return in the system and gave me peace of mind instead of waiting months wondering.

I've got to admit I was wrong about Claimyr. After dismissing it as a scam, I was completely desperate when the IRS sent me a notice claiming they never received my mailed documents (despite my delivery confirmation). I reluctantly tried the service, fully expecting to waste my money. To my shock, I got connected to an actual IRS representative in about 20 minutes, after trying unsuccessfully for WEEKS on my own. The agent was able to confirm my return was actually in their system but had been filed under an incorrect tracking number. They corrected it while I was on the phone and canceled the non-filing notice they had sent me. Saved me from potentially thousands in penalties and months of additional stress. I'm still stunned it actually worked.

Don't overthink this - I've sent plenty of returns using Priority Mail with no issues. But make sure you're sending it to the CORRECT IRS address! The mailing address varies depending on your state and whether you're enclosing payment. Double-check on the IRS website before sending anything.

Just wondering - have you considered scanning everything and e-filing instead? Even for prior year returns, there are options like TaxAct that still allow e-filing for previous tax years.