topic Re: Mail can't verify the identity of the server 'imap.plus.net" in Email

Mail can't verify the identity of the server 'imap.plus.net"

ann3 — Mon, 11 Aug 2025 11:43:28 GMT

Tried to use my Mac Mail client this morning to be told that "Mail can't verify the identity of the server "imap.plus.net". The certificate for this server is invalid... " etc.

The certificate appears to be new, as it runs until 10 August 2026. It seems to have the right words in the right place - but what do I know? Can anyone with a better understanding please reassure me that it is OK to trust this server with the new certificate?

Re: Mail can't verify the identity of the server 'imap.plus.net"

j123 — Mon, 11 Aug 2025 11:37:29 GMT

Same on POP. Can't collect mail:

mail.plus.net
Issued by: GeoTrust G5 TLS RSA4096 SHA384 2022 CA1
Expires: Monday, 10 August 2026 at 00:59:59 British Summer Time
x This certificate was signed by an untrusted issuer

Re: Mail can't verify the identity of the server 'imap.plus.net"

jab1 — Mon, 11 Aug 2025 11:40:46 GMT

Can you screenshot the whole of the notification - the one from @ann3 is missing the foot?

Re: Mail can't verify the identity of the server 'imap.plus.net"

ann3 — Mon, 11 Aug 2025 11:41:37 GMT

That's the one. I tried to add a screengrab of the certificate details, but for some reason the link only points back to my file manager, and won't load the image. Not my best Monday morning...

Re: Mail can't verify the identity of the server 'imap.plus.net"

ann3 — Mon, 11 Aug 2025 11:42:06 GMT

I'll try again - I didn't think it was loading.

Re: Mail can't verify the identity of the server 'imap.plus.net"

j123 — Mon, 11 Aug 2025 11:52:49 GMT

Rebooted into macos Monterey to see if it was because I was on an old system, but getting the same message.

Screenshots attached (macos doesn't make it easy).

Re: Mail can't verify the identity of the server 'imap.plus.net"

jab1 — Mon, 11 Aug 2025 12:01:58 GMT

I can't see an 'untrusted issuer' in there, but I'm no I'm no expert in this field.

@Townman ?

Re: Mail can't verify the identity of the server 'imap.plus.net"

Townman — Mon, 11 Aug 2025 12:05:51 GMT

@ann3

Not seeing any issues here. Are you configuring a new client? Has this worked previously?

Which email client?

I am a tad suspicious of the coincidence of the end date with today's date ... it is darned close to being just under a year to expiry.

To confirm, your email client is using the correct server names?

mail.plus.net
imap.plus.net
relay.plus.net

Some email clients try to use server names based on the the email address ... or other guess work which will give rise to certificate issues.

Re: Mail can't verify the identity of the server 'imap.plus.net"

j123 — Mon, 11 Aug 2025 12:05:59 GMT

It's the DigiCert Root G5 certificate that's not trusted.
Possibly a server configuration problem?

Re: Mail can't verify the identity of the server 'imap.plus.net"

Townman — Mon, 11 Aug 2025 12:16:12 GMT

@plusnettony

Would you have any idea what is going on here please?

My email clients are not flagging up any issues.- Outlook365 and iosMail on iPhone - all configured on secure ports.

Re: Mail can't verify the identity of the server 'imap.plus.net"

j123 — Mon, 11 Aug 2025 12:23:49 GMT

I'm wondering if it's a problem with the root certificate installed on older macOS systems. I'm running macOS Monterey (12.7.6).

I've just checked on an iPad running the latest system and mail is working ok.

My install of Monterey is up to date, but it's an old OS. Perhaps older macs need to update the root certificate? (Somehow.)

Update: Scrub that. It says DigiCert TLS RSA4096 Root G5 Expires: Sunday, 14 January 2046.

Re: Mail can't verify the identity of the server 'imap.plus.net"

ann3 — Mon, 11 Aug 2025 12:54:16 GMT

@Townman

Thank you. I haven't changed any settings overnight. I'm not configuring a new client. I'm using Mail, which is the Mac mail client. It was working fine when I last used my desktop Mac on Friday. Also working fine on my iPhone and my iPad over the weekend. However, I got the same message in Mail on my iPhone this morning.

Re: Mail can't verify the identity of the server 'imap.plus.net"

Townman — Mon, 11 Aug 2025 13:00:17 GMT

@ann3

So no changes - it was working yesterday, it is not today. That aligns with the less than a year to expiry, as though the expiry date was being treated as 2025, not 2026!!

You have indicated some commonality with @j123 - both Apple environments. They report theirs are being somewhat mature. What versions are you on?

I have an old iPad (iOS 12...) which continues to work fine.

Is this relevant - Why do I get the 'This root certificate is not trusted' error – Support

Re: Mail can't verify the identity of the server 'imap.plus.net"

Scallywag1 — Mon, 11 Aug 2025 13:08:29 GMT

I have exactly the same problem, and it also started to happen this morning. Email was working fine yesterday.

I'm also on a Mac - running MacOS Ventura, so not that old.

My iPhone email is still running perfectly, so this only appears to be affecting Mac Mail.

Re: Mail can't verify the identity of the server 'imap.plus.net"

ann3 — Mon, 11 Aug 2025 13:11:30 GMT

@Townman

Thank you. Running an ancient OS version on the desktop and iOS on the iPhone has just this year gone out of scope of updates. However, iPad is current - just checked Mail on that, and there were no problems. So things are rather pointing in that direction. Need to be someone else NOW but will check the link re adding certificate to the Mac later... and thanks.

Btw, I think someone has confirmed that the certificate itself is to be trusted, which is the other issue here.

Re: Mail can't verify the identity of the server 'imap.plus.net"

Townman — Mon, 11 Aug 2025 13:12:27 GMT

@Scallywag1

A warm welcome to the forums.

Three people, same problem all on Macs ... starting to look like a Mac environment issue. That is out of my skill set!! However, I would recommend looking at Apple's support forums ... and the link above.

I have tagged a member of staff here as a back stop, but I am starting to suspect that the issue is elsewhere.

Re: Mail can't verify the identity of the server 'imap.plus.net"

MisterW — Mon, 11 Aug 2025 13:19:10 GMT

I'm wondering if it's a problem with the root certificate installed on older macOS systems. I'm running macOS Monterey (12.7.6).

@j123 I think you've hit the nail on the head there. The certificate for mail.plus.net ( and imap.plus.net ) have recently been reissued and the new chain references an updated Digicert Root certificate which is not preset in the root cert store of some older OS.

This provides some more details of which root certs are installed in various OS versions https://support.apple.com/en-gb/103272.

It also doesnt quite explain why @Townman s IOS12 works though ?

Re: Mail can't verify the identity of the server 'imap.plus.net"

j123 — Mon, 11 Aug 2025 13:19:24 GMT

Looks like there is a missing Root G5 certificate on older macOS systems.

I downloaded the DigiCert TLS RSA4096 Root G5 certificate from Digicert's website. <https://knowledge.digicert.com/general-information/digicert-trusted-root-authority-certificates#g5roots>

I imported it into Keychain Access and changed the trust to 'Always Trust'. Quit and relaunched Mail.app, and now all is working.

Re: Mail can't verify the identity of the server 'imap.plus.net"

Scallywag1 — Mon, 11 Aug 2025 13:38:19 GMT

Thankyou j123! - followed your instructions and now mail is working again.

So, is this an entirely safe way to fix this issue, or just a work-around?

Re: Mail can't verify the identity of the server 'imap.plus.net"

Townman — Mon, 11 Aug 2025 13:50:04 GMT

@MisterW wrote:

It also doesnt quite explain why @Townman s IOS12 works though ?

ooops!!

But it does not - one was not looking at the right email account!!!