A friend texted me today saying he replied to an email that I had sent him earlier today and had gotten an undeliverable reply.

He texted me the message he got back, which listed all three Shaw emails that I had included in my original, but not the fourth address which was NOT a Shaw account, nor the other non-Shaw emails that my friend had added onto his reply:

<address1@shaw.ca>: host smtp.glb.shawcable.net[64.59.134.8]) said: 550 5.1.0 <friend'saddress@me.com> sender rejected (in reply to MAIL FROM command)

<address2@shaw.ca>: host smtp.glb.shawcable.net[64.59.134.8]) said: 550 5.1.0 <friend'saddress@me.com> sender rejected (in reply to MAIL FROM command)

<address3@shaw.ca>: host smtp.glb.shawcable.net[64.59.134.8]) said: 550 5.1.0 <friend'saddress@me.com> sender rejected (in reply to MAIL FROM command)

Again, it did NOT list any of the non-Shaw emails.

Was also doing some online banking last night, and one of them had a message saying they needed a valid email for my account - it had been the Shaw one and had been working fine for over two years now. So they too had tried to send me something and had gotten rejected?

Are Shaw's mail filters getting overly aggressive and filtering out legit email? Or is one of your mail servers getting blacklisted? Or is something getting flakey at your end?

NOTE: My friend just tried to send it to me again - it never arrived (and I checked though webmail as well), and yet I've been getting other emails during this time. He was able to send it another non-Shaw email address of mine, so not something at his end.
And TWICE NOW, my Mac Mail program has popped up a message asking for my password for my Shaw account, and yet other times it is getting email no problem?

WHAT'S GOING ON?!?!