Apple mail has STOPPED fetching messages BUT will send

[#1]

Hello

As of 8 August 2025, Apple mail has been displaying an error message in the following terms:

'Mail can't verify the identify of the server mail.plus.net.  The certificate for this server is invalid.'

I should say that I am using an ANCIENT iMac and am using the latest version available.  I have checked for system updates (didn't expect any) and the only thing is iTunes that I have stopped using anyway.

I have seen suggestions to delete the plusnet email account and re-add, but I don't want to do that in case my thousands of emails are permanently lost.  I don't know where to look for the certificate or how to identify it even if found.

Any pointers or input from the plusnet tech heads would be appreciated.

Many thanks.

[#2]

@perplexed1 its being discussed here https://community.plus.net/t5/Email/Mail-can-t-verify-the-identity-of-the-server-imap-plus-net-quot/...

[#3]

🤔 six pages with no definitive fix.  plusnet tech should be looking behind the scenes and not sitting by leaving users to stumble in the dark.

[#4]

Indeed a long thread ... but it is Apple who have not updated their mature devices with essential security certificates.  Have you asked Apple tech to "look behind the scenes ... rather than leaving THEIR users to stumble in the dark"?

Sadly as the world rolls out new security certificates using industry wide current root certificates, we are likely to see more and more legacy platforms made obsolete ... all for the sake of equipment vendors offering no forward path for installing the current root certificate.

Yes it is deeply technical ... as are most things connected to systems security ... that is intrinsic to making them secure!!

[#5]

Thanks for your response which was at least not a lot of techno-babble.  On the other thread, someone from plusnet said they are aware of the problem, but there is no update.  Apple is no help at all.

Ultimately, the solution might just be to dump Apple mail in favour of something else, but this may mean that this becomes an archive rather than an active program.

[#6]

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@perplexed1 wrote:

Ultimately, the solution might just be to dump Apple mail in favour of something else, but this may mean that this becomes an archive rather than an active program.

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That is not a solution; dumping the mature Apple platform might be the solution, though there are plenty of android platforms which do not have current root certificates distributed either.

This is not an issue relating to the email application, but the environment within which the application is being run.  Put any other email client on that environment and you will face the same issue.  The cause of which is that the latest root certificates are missing from the device and they are required to verify the email server's certificate.

The right solution is to get the current security certificates installed on the devices by / from the device's vendors.  There is a slim alternative mitigation, but that effectively requires Plusnet to down-grade the robustness of its security standard.  That might mitigate this issue, but the same brick wall is just around the corner for the next service to use a full-on current G5 root certificate.

[#7]

'The right solution is to get the current security certificates installed on the devices by / from the device's vendors.'

This is an ANCIENT iMac desktop.  Where would I go for the 'current security certificates'?

[#8]

Ask the product vendor.

[#9]

I've a 2007 MacBook and that has out of date certificates which seem to prevent any use of a secure browser window.

I went round the loop of attempting to update certificates on the machine and failed.

I think the key thing to work out is if the mail is really all on your machine and nowhere else (POP3) or just a copy (IMAP).

Then perhaps get a replacement Mac. I can recommend the current Mac Minis, I've an M2.

[#10]

Thanks for your input BUT I think the problem really lies with plusnet since I am able to send mail using Apple's native client.  This business with certificate(s) is muddying the waters.  IF I can send, why not receive?

My 2011/2012 aluminium iMac desktop was working fine up until 8 August when someone or something broke whatever.  I'm not a technician and can't scramble about in the system since I don't even know what the problem looks like.

[#11]

This business with certificate(s) is muddying the waters.  IF I can send, why not receive?

There are different servers for sending and receiving with different SSL certificates. The sending servers (relay.plus.net) are not due to have their certificate renewed yet, whereas rhe receiving ones (Imap.plus.net & mail.plus.net) have had renewed certificates.