The Blessings of Friendship

Rabbi Yehoshua ben Levi said: One who sees their friend after thirty days have passed since last seeing them recites: Blessed…Who has given us life, sustained us and brought us to this time. One who sees their friend after twelve months recites: Blessed…Who revives the dead. As Rav said: A dead person is only forgotten from the heart after twelve months have elapsed, as it is stated: “I am forgotten as a dead person, out of mind; I am like a lost vessel” (Psalms 31:13).

1. One who sees their friend after thirty days recites shehecheyanu, and after twelve months, one blesses mechayei meitim. And this is in a case where the person is very dear to them and they are happy to see them.

2. One who has never seen their friend before, even though they have sent letters to each other and are happy to see them, does not make a blessing upon seeing them.

...This refers to a case where they did not receive letters from them, but if they received a letter, they do not recite mechayei hameitim. Regarding shehechayanu, though, there is no disagreement: even if they received a letter within the 30 days, they bless shehecheyanu. The reason for this is that the blessing of shehecheyanu comes from the joy of seeing them face to face, whereas the blessing of mechayei hameitim comes from the fact that you now have proof they're alive (and therefore, since they already knew they were alive from letters or hearing from others, the blessing of mechayei hameitim is not relevant)...

4. Mechayei HaMeitim - And then one does not bless "shehecheyanu." And the reason for this blessing was written in Chidushei Agadot: each year, a person is judged for life or for death on Rosh HaShanah and Yom Kippur. So if you saw someone after this Rosh HaShanah and Yom Kippur but did not see them again until after the next Rosh HaShanah and Yom Kippur, they have gone through judgment about whether they will die or not. Thus, one says "Blessed...who revives the dead," because they were saved from being sentenced to death on Rosh HaShanah and Yom Kippur.

5. They have sent letters - This is to say that even if they sent letters to each other and thereby came to love each other, nonetheless, since they did not connect face to face, their love is not elevated to the extent that they would be overjoyed at seeing each other.

The Pri Megadim wrote that if one was overseas and heard that their wife gave birth, and is now seeing the baby, one blesses shehecheyanu (or mechayei hameitim if it is 12 months later)-- for certainly one has joy in their child, even if they've never seen them before.