Unable to send email containing YouTube link

[#1]

I'm trying to send an email and keep getting the error (from my mail app)...

"Cannot Send Mail - Sending the message content to the server failed."

I assume it's erroneously being refused by Plusnet's outgoing spam catcher - please could someone confirm this and how it can be fixed. Many thanks.

Some boring details:

• Message - just text with a link to a YouTube video (Marvel's latest official Thor trailer - looks fun!).
• Testing - sending exact same message without url - works.
• Testing - sending exact same message but with a link to my own website - works (thank goodness!).
• POP3 email sent via Plusnet's SMTP (relay.plus.net) using Mail in macOS 10.12.4

Now I appreciate the need to block email sending links to dodgy websites, but a blanket ban on YouTube!?

Many thanks in advance for any input people may have.

[#2]

Try changing the YT link so it doesn't appear as html code.

[#3]

Thanks @Gel for taking the time to reply.

There was no html involved, simply a plain text message with the url bookended with angle brackets (pretty standard stuff, I believe).

Interestingly, I've just sent a new identical test email, along with one of yesterday's rejected test emails; and they were both sent & received without error. Nothing has changed at my end; no Mail quits, restarts or machine reboots etc. - strange.

Maybe something has been tweaked behind the scenes, or maybe I somehow unwittingly angered the interweb gods yesterday!? <shrug>

A tad annoying that I'm none the wiser, but it appears to be working now so...

Cheers!

[#4]

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toggie101 wrote:maybe I somehow unwittingly angered the interweb

Are you, like me, using MS Outlook? I was scratching my head as to why nothing would go out of my outbox earlier until I realised I had got a pending update/restart. I applied it manually and now mail is being sent normally again.

For me this is the second month in a row that MS Updates have screwed my system temporarily.