Email failure: what on earth does this war'n peace alert mean?

[#1]

An error occurred while sending mail. The mail server responded:  5.2.0 STOREDRV.Submission.Exception:SendAsDeniedException.MapiExceptionSendAsDenied; Failed to process message due to a permanent exception with message Cannot submit message. 0.35250:0A00B284, 1.36674:0A000000, 1.61250:00000000, 1.45378:02000000, 1.44866:3B020000, 1.36674:0E000000, 1.61250:00000000, 1.45378:40020000, 1.44866:24010000, 16.55847:CA030000, 17.43559:0000000004020000000000000000000000000000, 20.52176:140F58880000001043050000, 20.50032:140F58887617101000000000, 0.35180:02000000, 255.23226:0A6F0000, 255.27962:0A000000, 255.27962:0E000000, 255.31418:0F6F0000, 0.35250:A5030000, 1.36674:0A000000, 1.61250:00000000, 1.45378:02000000, 1.44866:1A000000, 1.36674:32000000, 1.61250:00000000, 1.45378:1F000000, 1.44866:01000000, 16.55847:86000000, 17.43559:00000000E0020000000000000100000000000000, 20.52176:140F588800004010F1030000, 20.50032:140F5888761710100A000000, 0.35180:00000000, 255.23226:02000000, 255.27962:0A000000, 255.27962:32000000, 255.17082:DC040000, 0.27745:00000000, 4.21921:DC040000, 255.27962:FA000000, 255.1494:7A050000, 0.38698:00000000, 0.37692:05000780, 0.37948:00000000, 5.33852:00000000534D545000000100, 4.56248:DC040000, 7.40748:010000000000010BB877FE04, 7.57132:000000000000000020BEC510, 1.63016:32000000, 4.39640:DC040000, 8.45434:00000600D785EE12000000000000000000000000, 5.10786:0000000031352E32302E323133362E3030303A564531505230324D42353432343A31306335626532302D316337342D343664332D386331342D62333631303030373664323600000000000000, 255.1750:03001736, 255.31418:A7050000, 0.22753:0A00D685, 255.21817:DC040000, 4.60547:DC040000, 0.21966:0A00DC85, 4.30158:DC040000 [Hostname=VE1PR02MB5424.eurprd02.prod.outlook.com]. Please check the message and try again

The email in question was from my Plusnet account o my daughter, a Plusnetter too, and contained links to shops, I need her to take me to. My email client is Thunderbird. I made three attempts to send it.

[#2]

Problem dealt with. I'll come back later with details.

[#3 · Accepted solution]

Although I was sending mail from PN to PN. for some unfathomable reason the SMTP credentials for my Hotmail account, which uses Outlook SMTP had gone AWOL.

A mystery for someone to explain, maybe, if  he wishes, but solved.