It isn’t the easiest thing to collect a good mailing list event though emails make things swifter than posting ( not the least concerning money).
Nor are people willing to give out theirs. This may be because they have people on their lists who don’t want more art invites, it’s a question of integrity.
Nevertheless, look up institutions and galleries on the web, under contact and start collecting the addresses that way. It’s a bit tedious work, and you will need to update your list once and again. Also look up websites for art critics, curators, art organisations in your area, and whom seem relevant to you. When you send your pressrelease do not make attatchments post your invite and images withing the email. Not all email accounts provide this, but gmail does for one. For some reason some emails with attachments will look like spam and never be read.
Maybe you shouldn’t send them all in one go either, because then the addressees will have your list and know who’s on it and so forth.
Give it a thought. Another tip. Don’t send your emails in the afternoon but rather late at night or in the morning, because you don’t want people to read it in the afternoon. Especially journalists read better with fresh eyes…