YAMM has unfortunately been gradually reducing the effectiveness of it's free service.
Initially, you could send 50 emails a day and get this bumped up by an extra 50 for each person you referred to also use YAMM. Then YAMM took away the referral bonus and capped it at 50 emails a day.
In the past week or so, YAMM has appeared to cap the daily limited at 20 emails a day so it's not really worthwhile using the service.
I was tempted to pay for YAMM because of the ability to schedule emails but the scheduling functionality looks very basic. I'd like to be able to schedule batches to go out each day but YAMM appears to only let you schedule one batch at a time.
There are other free ways to send out emails which I'll need to get back into.