Proper communication is whatever they will accept. The question is how do you find this out? Ask them. Send them a list of ways you can be contacted in your welcome email and ask them what is most convenient for them.I realize that if they don't respond this is very difficult, but you can try and find them in some social media situation and ask them if emailing is the best way to contact them. If you don't get an answer then, drop it, and continue sending them emails.
If they contact you after the first email in which you sent a listing for the different methods of contact, use the one they suggested. Perhaps you could do a survey, using the methods available and send it to all of your PSA's and then you would have a better idea what is best for them.
Never,never make assumptions in any kind of sale situation. Use what is available to you and ask what is best for them.If you contact your new PSA in every way you can utilize, the one they respond to is probably the one they would prefer, but ask anyway. Give them control whenever possible so you can find out what is best for them. If they don't respond, the most beneficial way is to do the weekly letters. Some people who don't respond at first might respond when they feel they can trust you to contact them regularly.
Proper communication is whatever they will accept. The question is how do you find this out? Ask them. Send them a list of ways you can be contacted in your welcome email and ask them what is most convenient for them.I realize that if they don't respond this is very difficult, but you can try and find them in some social media situation and ask them if emailing is the best way to contact them. If you don't get an answer then, drop it, and continue sending them emails.