Think: Cocktail attire meets garden party. For women, airy and breathable florals; generally not floor length (mini or midi is good). Reminder to wear a thicker heel if possible. For men, tux is not necessary. Jackets don't need to match pants. Maybe not khakis, but "Slackies"? In general, we know that many people will be traveling before and/or after the wedding so we don't want you to have to schlep a bunch of bulky stuff around that you are only going to wear for the wedding. At the end of the day, if it makes you happy to wear something, then we are happy.
From Milan Malpensa (MXP), you can take the Malpensa express into Milan city center (Milano Centrale Station). This takes about 1 hour. Link: https://www.malpensaexpress.it/en/ From Milano Centrale station, take a train to Varenna-Esino station, direction "Lecco - Sondrio - Tirano." No need to purchase tickets in advance. This train can take 1-2 hours. https://www.trenitalia.com/