If you are filing a bunch of missing tax returns, should I mail them all together or mail some and e-file the last three years that are eligible for e-filing?

I would mail the returns together in one package. The reason for doing so is that you want the returns to be processed and billed around the same time. If you e-file some and mail in others, the e-filed returns will be billed and go into collections before the mailed returns are even opened and processed. This can create the situation where you need to deal with collections, yet cannot do anything because the taxpayer is not in compliance due to the IRS\’s inability to process the hard copy returns. Better to submit them all together, let them be opened together and processed together.