I need to take a mid-trip intra-European flight to northeastern Italy later this year and plan to visit Ravenna. I can see I need to investigate flights into Bologna, something I hadn't considered before. I really appreciate the heads-up on that possibility.
The Milan option could be useful for folks coming from North American origins that don't have good connections/fares into Venice. However, there seem to be very, very few routings that don't require a transfer. I only found one, a 6:15 PM departure from Milano Centrale, which I think would be much later in the day than most travelers would want.
The other issue is that Malpensa Airport is quite far from the city. Adding the additional time to get from the airport into the city and make a connection at Milano Centrale drives the minimum total travel time above 4 hours with only one exception I could find: a 3 hr. 50 min. trip departing at 9:26 AM and requiring 3 changes--which would be a lot for me when jetlagged.
Fares from Milan Malpensa to Ravenna seem to run from 33 to 76 euros, and the cheap trains I looked at for early June had travel times well over 4 hours--more like 5-1/2 and up.
By comparison, bus service between Venice-Marco Polo and the Venice-Mestre train station is relatively frequent (4/hour), fast (17 to 25 min.) and not grotesquely expensive (8 euros). Once you're at Mestre you have a trip to Ravenna that generally takes 3 to 3-1/2 hours with a single change. The fares I saw for my random day in June ranged from 14.40 to 28 euros. The 14.40-euro fare is for an all-regional trip via Ferrara. An all-regional trip via Bologna (additional miles and a bit slower) costs 18.20 euros. Those all-regional routings can simply be purchased on the day of travel, so those fares are always available. Overally, traveling from Venice-Marco Polo to Ravenna seems to be cheaper and not much slower (potentially faster) than from Milano-Malpensa.
Edited to add:
For my own purposes I just looked at what is involved in getting from the Bologna Airport to Ravenna. The answer is: not much. It looks really great. From the airport to the city there's a little driver-less train (similar to what airports use). It runs 4 to 8 times per hour and takes about 8 minutes. The fare is 9.20 euros.
Then from Bologna Centrale to Ravenna you have direct trains taking 62 to 92 minutes; most are 70 minutes. Even on Sundays there's at least one train per hour. The fastest options are all regional trains with never-changing fares. Tickets are 7.35 euros.
This looks like a great option for cruisers whose origin airports have good connections and fares to Bologna. (I have no idea how common that might be.)