I can also send mail from Virgin Media on the web, using the username and password that I’m being told is incorrect!
Unfortunately when email apps fail to authenticate with the SMTP email server they often cloud the issue by defaulting to reporting a password error even though the problem lies elsewhere.
The symptoms you report are the classic signs of emails sent from an email app on your VM home network being blocked because the IP address of your home network is on a spam blocklist. That is usually because there is malware on a smart device on your network that is sending out suspicious, spam traffic.
You can check that by following these simply steps:
Your IP address may well be listed on the PBL (Policy Block List) and flagged up as an advisory but that is to be expected and is not the reason you cannot send emails from the email app on your Apple devices.
However, post back if Spamhaus reports that the IP address is listed on any other blocklists, such as Spamhaus' Exploits Block List (XBL) for example.
As a workaround, if your VM IP address is on a spam blocklist, you should still be able to send VM emails from iPhone when you are connected using your mobile data network (rather than your VM wifi). That is because it will be using a different IP address which has been allocated by your mobile provider.
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