Outlook can't send email to one contact, but web based mssgs work fine

As the title says, I use Microsoft Outlook '07 to access my Roadrunner and AOL POP accounts. If I send email from either account to one particular friend who uses windstream.net, and accesses his mail through Windstream's web mail page, it disappears without any trace that I can find. Not only doesn't he receive my newly composed messages, but he does not receive my direct replies either. That rules out a misspell. There is no evidence other contacts are not receiving my emails. I first thought maybe he had me blocked, however if I go to either of my two accounts' web based email pages, he receives my messages just fine.

And I always receive his emails. The only odd thing that might be a clue is that, since this began, about half of the email he sends me now, whether I view them in Outlook or on the web, is in plain format with system fonts. Sometimes they come to me in HTML.

I never get any delivery failure notification either. The last time he got one of my emails is when I sent out a July monthly newsletter to about a hundred people including him. I usually get the same few failure notifications because some of our members' addresses have changed or can't be found... the usual reasons, and I need to update my distribution list. But he got that letter in July, and that's the last time I've been able to send him anything through Outlook on either AOL or Roadrunner. But both of those ISPs always deliver mail to him if I use their respective web pages to send it. What could be going on? I'm thinking it's something with his Windsream.net service. But if he had me blocked, it would also reject me when I send from the web.

This is an odd one. can anyone help?
Thanks,
Rusty

This sounds like an issue with the ISPs and their "blacklist" anti-spam software.
They may be reacting to some combination of words &/or pictures that match a spam pattern.

For example, last week, I transferred some money to my sister-in-law's bank account. My bank's website has a feature that allows an automatic email to be sent to the recipient, advising of the transfer.

Her ISP rejected the message as matching that of a "Nigerian Prince" scam!

Haha, that's funny. Just a moment ago I told one of the guys on my mailing list I was trying to prove I'm not a Nigerian Lawyer. Don't know if he got it or not, I asked him to ping me if he did.

I'm going to call Time Warner, who provides my keyhole into the internet, and see if they can help clear my name.
Strange how I'm only semi blocked. Once in a while, a message gets through. Two of about 10 tries got through to my wife's email last night.

Thanks for your reply.
Rusty

The newsletter I sent out contained one PDF of about 450MB

An attachment of 450MB is pretty large, many ISPs, both sending and receiving, will have limits on attachment size, may be as little as 2MB. I'd think it better to use something like DropBox to upload then send the link to it. Actually, that seems to be quite a large file size for a .pdf file, must be a lot of images in it.

Oops, I meant 4.5MB. Yeah, 450MB would never make it out of the door. I'll edit my post.
Sorry.

I think I'll start sending everyone a dropbox link to the newsletter, rather than an attachment.

Rusty

This thread is Semi-Solved, but I'm starting a new one to un-muddy the water, so to speak.
Thanks for the replies.
Rusty