Mark B,
I just received a membership request from an unfamiliar email address on
a restricted group that I set up on Groups.io. I am hesitant to send an
email out from my personal email address out of concern that this is
from a spammer and my personal email address will be added to a spam
list.
Groups.io has a feature for just this purpose.
Go to the Members page of your group, and select Pending Approval. That should show a list of those who've applied but not yet been approved. Put a check mark on the row of that unfamiliar email address, and use the Actions menu to select "Send Message".
That will bring up a message composition window. Change the From field to your group's +owner address instead of your personal address. Write your message, and send it. Use one of the Bcc checkboxes if you wish to receive a copy of your message, one won't be saved on site (that's a wishlist item).
Shal
Shal Farley