You could start (or end) with "previously posted on NotATether.com's mailing list", but that might make it look more like spam than without the link.
Yeah, I'm not sure if that's even possible since there's no such thing as a permalink to an email.
I think you are just worried about increasing traffic for your website [my guess] because maybe some people will think that you will take advantage of this forum to increase your site's traffic and profit through advertising. Obviously it will benefit you, but when the content you present is actually quite useful, I don't think you need to worry about that.
I don't have advertising on my website (yet) - traffic levels are currently way too low for that. I do admit that this is ultimately supposed to increase traffic though - I've been trying lately to get users to stay on my website because the vast majority just come from Google Search, stay for a minute or two, and then leave and never return:
(and strangely, the majority of search queries are for "wallets" and "hardware wallets" - I clearly need to diversify that.)
If you just repost the material you send through your newsletter or mailing list, I am not sure how can be proved whether it is plagiarism or not. received mail is somehow a personal matter after all, and none of us can have a real legit insight into the content of the email.
I think Mailchimp lets me
download a copy of emails I send through the mailing list, but I never tried it before.