topic Re: SMTP Error (535): Authentication Failed in Email

SMTP Error (535): Authentication Failed

-Simon- — Mon, 15 Sep 2025 13:53:48 GMT

I have an @ic24.net email address and from some point this morning I am unable to send email via a mail client or via Webmail.

I am able to receive email fine via mail client and Webmail, but sending via either method fails with an SMTP authentication error.

The Webmail client gives the error SMTP Error (535): Authentication Failed and my mail client (iPhone native Mail app) gives a similar error (username or password incorrect)

I know there is some sort of mail migration going on and wonder if Plus.net haven't added the ic24.net domain to the list of authorised sending domains or something similar?

The last email I sent successfully was 09:23 this morning (15/09) and the next one I tried to send around midday failed, and I have been unable to send since.

Re: SMTP Error (535): Authentication Failed

Townman — Mon, 15 Sep 2025 14:44:11 GMT

For the avoidance of doubt - you can login to webmail, receive but not send?

@plusnettony - has ic24 entered the migration programme?

Re: SMTP Error (535): Authentication Failed

-Simon- — Mon, 15 Sep 2025 14:46:28 GMT

Thanks for the reply, yes I can login to Webmail, and login using my iPhone Mail Client and receive emails. Just unable to send via either method.

Re: SMTP Error (535): Authentication Failed

Steve-P — Mon, 15 Sep 2025 15:04:29 GMT

You're not alone - I also use an ic24.net email address and have the same problem - Webmail or Outlook on Android/Windows in my case.

Re: SMTP Error (535): Authentication Failed

plusnettony — Mon, 15 Sep 2025 15:16:51 GMT

Thanks guys, an ICScoland issue has been raised, suspect it is the same problem. If you're username isn't linked to your forum profile, can you PM it to me please.

Re: SMTP Error (535): Authentication Failed

TonyParker — Mon, 15 Sep 2025 17:22:38 GMT

I'm in the same situation. I have an IC24 email address and can receive emails on my android phone, webmail and Windows11 Outlook.

Since today I can't send emails from any of them.

Re: SMTP Error (535): Authentication Failed

masrjk — Tue, 16 Sep 2025 07:11:33 GMT

My email address is <Redacted>@ic24.net

All my outgoing emails stopped and I had issues with outlook on my laptop.

Moderator's note:
Personal information removed from a public forum (to an area that staff can see).

Re: SMTP Error (535): Authentication Failed

plusnettony — Tue, 16 Sep 2025 07:50:06 GMT

Thanks all. anyone who hasn't sent me a username, how you've tried (i.e. client / webmail ) and times you attempted it, please do so and I'll forward on the examples. Thanks all.

Re: SMTP Error (535): Authentication Failed

stuck — Tue, 16 Sep 2025 11:08:01 GMT

post deleted by user, posted on the wrong topic, sorry

Re: SMTP Error (535): Authentication Failed

Townman — Tue, 16 Sep 2025 15:26:00 GMT

Can everyone reporting this issue please retest and advise if there are still issues. An issue mitigation elsewhere might have also mitigated this experience.

Thank you.

Re: SMTP Error (535): Authentication Failed

-Simon- — Tue, 16 Sep 2025 15:39:28 GMT

I have just tried sending two emails via the Webmail client, and received the SMTP Error (535): Authentication Failed message.

BUT, I then tried sending an email via my iPhone native mail client and it sent fine.

Afterwards, I tried again using Webmail and it failed again so looks to be just Webmail that's not working now.

Re: SMTP Error (535): Authentication Failed

TonyParker — Tue, 16 Sep 2025 15:33:04 GMT

My emails are now sending again. Thanks to whoever fixed whatever.

Re: SMTP Error (535): Authentication Failed

TonyParker — Tue, 16 Sep 2025 15:44:12 GMT

I'll qualify my previous response, I've now checked webmail and that still failed with SMTP Error (535).

Re: SMTP Error (535): Authentication Failed

Townman — Tue, 16 Sep 2025 15:54:05 GMT

@-Simon- thank you for the dual feedback - I have escalated the divergent behaviour.

@TonyParker is your failure with webmail or a local client?

Re: SMTP Error (535): Authentication Failed

TonyParker — Tue, 16 Sep 2025 15:57:08 GMT

Webmail

Re: SMTP Error (535): Authentication Failed

Townman — Tue, 16 Sep 2025 16:00:05 GMT

@TonyParker that matchs @-Simon- 's experience ... and I suspect matches my theory which I have escalated.

If you have an IMAP client configured on a local device, it should all work fine.

Re: SMTP Error (535): Authentication Failed

colbee — Tue, 16 Sep 2025 19:24:26 GMT

Add me to this issue also.

Re: SMTP Error (535): Authentication Failed

Townman — Tue, 16 Sep 2025 20:05:30 GMT

@colbee

Works with a local client, fails with webmail?

Re: SMTP Error (535): Authentication Failed

john_chandler — Wed, 17 Sep 2025 07:35:29 GMT

I have the same problem - just tried to send an email. I can login to Webmail just fine, but sending emails raises the SMTP authentication error.

Edit: this is using a plus.com address.

Re: SMTP Error (535): Authentication Failed

colbee — Wed, 17 Sep 2025 08:46:10 GMT

Hi,

Happens on webmail, Unable to try with a client at the moment . Same this morning.