completely OT re: Presto service

I've given my very elderly, computer-illiterate mother-in-law, in a faraway state, the Presto service. How it works: Her kids and grandkids can send e-mail and pictures to her Presto e-mail account. Grandma's "Presto printer" uses her phone line to dial into Presto's servers thrice-daily to pick up any e-mail, which is then printed out by the printer.

She really likes it and it sounds great; without Internet access, she can now receive e-mail. She doesn't need computers or training. And, spam is eliminated because only e-mail from approved senders is allowed to reach her account.

She is a very charming, smart woman, but no match for spammers (and would be shocked by porn mail), and I'm concerned that there is a flaw in the system. If malicious e-mail gets forwarded from the e-mail accounts of any of the approved senders, couldn't it reach her in-box?

I was thinking of telling all of her approved senders to switch to Gmail, because it is so good at eliminating spam. Am I being too paranoid?

Bob C