Check again. The VM305 error only arises for IPs listed on Spamhaus's SBL list. VM refuse to relay from such IPs because the SBL entry means that Spamhaus has detected that the IP is sending spam. All dynamically allocated IPs for residential use should be on the PBL because such IPs should not be running mail servers. So that listing doesn't cause e-mail sending errors.
Basically your network is infected with a spambot.
You could try your usual AV or malware detector, usually that draws a blank but they are not completely reliable indicators that you are infection free. And quite often use of the Free version of the Hola VPN is the cause (it isn't a true VPN but a peer to per networking software which is used to distribute spam). The other cause is a jail-broken Amazon Firestick - which has unapproved and unauthorised software on it.
Finally although the spambot may go quiet for a time (that is how they are programmed) and the SBL listing will then expire it will be back unless and until you deal with the underlying cause. And when it comes back VM will not send your mail.
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Hi, thanks for your prompt response. Sending mail was working this morning but has stopped again this evening. It's true I've added a wireless security camera, wireless speaker and wireless android TV device during lockdown. Not just as simple as disconnecting each and monitoring what happens then ....................
@Osteomen wrote: Don't worry; it was a rhetorical reply really, although Outlook working is puzzling. Maybe I just change to Outlook too ..............................
Please find the spambot, I beg you. Changing to an Outlook address won't stop the device behind your IP address sending the spam. Which it is doing now - sending spam to thousands of innocent people. No one can stop it except you - by finding it and cleaning the device. It is your network. VM are just protecting their servers by using the information from Spamhaus.
While searching for the spambot, you can use the VM webmail service in a browser to send using your VM email address. Webmail uses different security on different servers so does not get the VM305 error. Or you can take your device to a different IP address - using a data connection, neighbour's broadband or work or public place, etc.