In my opinion that depend from situation.
It is ok to send group mail if you have lot of PSA's that day or that period.
But if PSA's come occasionally you should write individual letter.
They will know than that they are imortant to you, they will feel special and wellcome.
So it is better for me to send individual.
if you send just group mail neww affiliates will think they are not umportant
and that's no good for your team.
In e-mail that I sent to each new member I give link form my FB profile, and if he/her add me as FB friend comunication is a lot easier.
In my opinion that depend from situation.
It is ok to send group mail if you have lot of PSA's that day or that period.
But if PSA's come occasionally you should write individual letter.
They will know than that they are imortant to you, they will feel special and wellcome.
So it is better for me to send individual.
if you send just group mail neww affiliates will think they are not umportant
and that's no good for your team.