Customs & Immigration in Dublin

You stay airside in Dublin - no immigration as you do not enter Ireland. Make your way to your connecting flight. Immigration will occur in Italy.

On your return, you do immigration as you enter Ireland and you also do US pre-clearance - US immigration at Dublin

Is Dublin to FCO on Aer Lingus? IF so, follow the green flight connection signs. There are folks around those signs usually if you have questions.

This is extremely helpful, thank you.

Yes, Aer Lingus. The green light tip is an excellent one!

When we arrive back home in Boston, will there be any other lines to wait in (customs?) once we deplane, or can we just get our bags and leave the airport?

I have been to and from Europe several times through Ireland and pre clearance in Dublin is like pre clearance in Canada. You do it all before you board your flight and then when you land stateside, you walk off the plane, get your luggage if not carry one & head for your ground transport just like you do for domestic flights.

https://www.aerlingus.com/prepare/airport-information/dublin-airport-terminal-2/connections/ This page on their website even has a picture of what the flight connection signs look like.

just get (y)our bags and leave the airport

You will have done everything in DUB.

1.5 hours layover seems is a little tight to me too, but remember you'll have the jet stream going that way so you'll land a little earlier unless you take off exceptionally late. If you have big concerns as you get closer to Dublin talk to your flight attendant and they can reassure you and/or help you get off the plane sooner.

Dublin Airport has a connections guide:

https://www.dublinairport.com/flight-information/connections/connection-guide

Your bags will be checked through to Boston. When you go through U.S. immigration in Dublin, you will be shown photos of your bags to confirm they are yours.

Be prepared to go through security in Dublin before your flight back to the U.S.

If flying from Dublin back to the United States then upon arrival in Boston you will depart the plane as you would a domestic flight. Grab your bags and go. Immigration (passport control) and customs will occur at Dublin’s airport.

Thank you for the links Laurie Beth and Frank II. All of these answers make the process clear to me & truly help in making an easy plan for pick up in Boston at the end a busy travel day. What a relief!

I deeply appreciate the tremendous knowledge, expertise and willingness to share that this wonderful forum provides. Looking forward to passing it on when possible!

Download and use the Mobile Customs app for when you return to Boston. We used it at JFK in March arriving back from Lisbon. We had a connection at JFK back to DTW and the app saved us a lot of time because there was no line at immigration.
More info here: https://www.cbp.gov/travel/us-citizens/mobile-passport-control.

Edited to add .. I see Dublin has preclearance to the U.S. so the mobile app will be unnecessary, but I highly recommend it for people returning to the U.S. without preclearance.