topic Re: Email send fails / SMTP Certificate in Email

Email send fails / SMTP Certificate

PhilipHeyes — Thu, 20 Aug 2026 07:52:45 GMT

Are you are seeing email setup or send issues that come out out of the blue . . .

I am seeing an SMTP Certificate rejection with Blue Mail app on Android when Certificate Check is enabled for either STARTTLS ( 587 ) or SMTPS ( 465 ). Sadly I am not getting any detailed explanation.

The Certificate rejection by Blue Mail occurs on the following SMTP servers that all appear to share
the Plusnet Certificate of relay.plus.net ( see CheckTLS attached ) :

Plusnet hosted relay.plus.net

Greenby hosted relay.force9.net |

Greenby hosted relay.metronet.co.uk

Greenby relay.metronet.co.uk is also named on this Certificate, but not affected, it lacks STARTTLS & SMTPS.

I was about to raise Greenby Ticket on this, but the issue does not affect versions MS Outlook or Thunderbird installed on MS Windows and it is not affecting Samsung Email app on Android, all are sending perfectly via relay.force9.net

My workaround is to use SMTP mail.enmail.co i.e. to avoid a Certificate that was issued to Plusnet & with this I am back in business with Blue Mail. Other options may be to disable Certificate check or Disable encryption, if permitted.

Quite a puzzle, what has worked well with relay.force9.net for 6+ months has ground to a halt in just one app.

email

IanfLowe — Wed, 19 Aug 2026 20:00:29 GMT

Out going emails stopped working on iPad incoming ok

Re: email

MisterW — Thu, 20 Aug 2026 06:13:06 GMT

@IanfLowe

Do you still have broadband with Plusnet ? or have you been moved to EE or moved to another ISP yourself ?

Re: email

IanfLowe — Thu, 20 Aug 2026 09:09:22 GMT

I have been told I will be moving to Greenby but that hasn't happened as yet.

My wife's email is still working on here iPhone though, but only when wifi is available for some reason.

I noticed looking at her settings that there may be an issue with the certificate but the certificate looked to be in date.

Re: Email send fails / SMTP Certificate

MisterW — Thu, 20 Aug 2026 10:18:54 GMT

Is it a missing intermediate certificate ?

Re: Email send fails / SMTP Certificate

PhilipHeyes — Thu, 20 Aug 2026 10:44:26 GMT

The start of the 2nd Certificate is obscured by the page header in the PDF.

Certificate #2 of 3 (sent by MX):
Cert VALIDATED: ok
cert not revoked by OCSP

Data:

Version: 3 (0x2)

Serial Number: 0e:a7:1a:b4:b9:b3:0f:67:f5:a6:e6:31:76:9d:ce:9c

Validity:

Not Before: May 26 00:00:00 2022 GMT

Not After: May 25 23:59:59 2032 GMT

Re: Email send fails / SMTP Certificate

MisterW — Thu, 20 Aug 2026 11:01:56 GMT

Not my area of expertise, but Yes, the certificate chain is correct but AIUI devices store root & intermediate certificates in their certificate store.

The fact that some devices work and some don't MIGHT indicate that the device that fails doesnt have one of the root/intermediate certs in its store and so cant completely validate the certificate chain

Re: Email send fails / SMTP Certificate

PhilipHeyes — Thu, 20 Aug 2026 11:20:47 GMT

I emailed a detailed question to Blue Mail support.

The bit that looks to have changed in my environment is the last update for Blue Mail app was on 15th of this month.

Re: Email send fails / SMTP Certificate

Townman — Thu, 20 Aug 2026 17:31:18 GMT

@plusnettony

Is this connected to the same issue we saw (IIRC) about 12 months ago when the certificates were renewed with root certificate which inhibited access by mature products whose vendors have not issued certificate updates.

i have a vague recollection that a date around now is a tad critical. I’ll try to check back in my records when back at my desk…

Re: Email send fails / SMTP Certificate

Mav — Fri, 21 Aug 2026 02:40:39 GMT

Moderator's note(s):

Two threads merged.

In the process one post by @PhilipHeyes removed as it looped back to this thread from the moved one.