topic Re: Unknown Sender errors from Greenby in Email

Unknown Sender errors from Greenby

mavison — Tue, 10 Feb 2026 10:35:32 GMT

Since our migration in December to Greenby the three Force9 email accounts for myself and my sone have worked, though not without some problems.

However, in the last week or so one son and myself have had problems sending some emails, as they have failed with 'Unknown Sender'. We all use @account.f9.co.uk addresses, not @account.force9.co.uk.

Greenby are now claiming that in order to send an email from eg name@account.f9.co.uk then name must either be the name of the mailbox, or have an alias for that name, and this has been the case since migration. This applies even to a catch-all mailbox.

My suspicion is that this was NOT the case until a week or so ago, and something has changed recently at Greenby.

It certainly was not a requirement of the Plusnet/Force9 email system.

Has anyone else had recent problems with Unknown Sender errors from Greenby?

Re: Unknown Sender errors from Greenby

balvack2 — Thu, 12 Mar 2026 19:51:53 GMT

Hi @mavison I'm still waiting for PN support to get back to me on why I can't send from my "mydomain.co.uk" identity in webmail which worked fine for a decade prior to migration. Given the feedback you were given I'm going to try and set up an alias, but I've gone through all the webmail settings and can't see how to do that. Could you advise? thanks

Re: Unknown Sender errors from Greenby

mavison — Thu, 12 Mar 2026 22:22:01 GMT

@balvack2

Create an alias by signing on to greenby.com.
Under Recent Products, click on Manage against your email domain to list all your mailboxes.
At the right of the line for the mailbox, click on the 3 dots to open a menu.
Then click on Aliases, and add the alias address you want to send from.

Re: Unknown Sender errors from Greenby

MisterW — Fri, 13 Mar 2026 08:56:02 GMT

@balvack2

why I can't send from my "mydomain.co.uk" identity in webmail

Is this domain hosted by Plusnet ? or is it just a personal domain registered elsewhere ?

Re: Unknown Sender errors from Greenby

balvack2 — Sat, 14 Mar 2026 00:29:17 GMT

@MisterW

It's a personal domain registered elsewhere. The 'identity' worked fine on webmail pre-migration. Leanne has looking into it but I guess she's been busy with all the other issues.

Re: Unknown Sender errors from Greenby

balvack2 — Sat, 14 Mar 2026 00:30:31 GMT

thanks @mavison but that only lets me create an alias with a myplusaccount.plus.com suffix, not mydomain.co.uk

Re: Unknown Sender errors from Greenby

MisterW — Sat, 14 Mar 2026 07:29:59 GMT

@balvack2

It's a personal domain registered elsewhere.

Thanks, that's what I suspected.

I would suggest that you arrange for the domain to be properly hosted and use the hosting servers to send mail. Being able to send from a domain address via the PLusnet servers in the past was really a loophole. I'd be pretty sure that the Greenby servers (like most others) dont have that loophole.

I'd suggest looking at Mythic beasts for hosting https://www.mythic-beasts.com/order/hosting?product=H-050

a basic Email account will only cost £20/yr

Re: Unknown Sender errors from Greenby

balvack2 — Sat, 14 Mar 2026 19:23:09 GMT

My domain is "properly" hosted. I can still send from my mail client OK, it's just the functionality in Webmail that has stopped working since the move to Greenby.

After more than a couple of decades with plusnet it looks like I'm going to have to bite the bullet and migrate our numerous mailboxes elsewhere. I'm certainly not going to pay £15/year to Greenby for a mail system that has reduced functionality and no customer support.

Re: Unknown Sender errors from Greenby

MisterW — Sat, 14 Mar 2026 19:49:24 GMT

My domain is "properly" hosted. I can still send from my mail client OK, it's just the functionality in Webmail that has stopped working since the move to Greenby.

so are you saying your domain is hosted by Plusnet ? I thought you said it was registered elsewhere ? It's been a very long time since it was possible to have a domain on a Plusnet account as 'hosting only'

AFAIK no accounts with hosted domains have been migrated

I suspect you can send from an email client because relay.plus.net is (temporarily) still routed directly to the Plusnet server, whereas webmail will route a migrated account to the Greenby server. Once the temporary situation is rectified, you won't be able to send from a client either

Re: Unknown Sender errors from Greenby

balvack2 — Sun, 15 Mar 2026 13:59:16 GMT

@MisterW

It's not hosted by Plusnet: it's hosted / registered elsewhere with email forwarding setup for about 10 mailboxes so name@mydomain.co.uk goes to name@myplusaccount.plus.com

It's really worrying that you say that it's only temporarily still working on my mail client. When is that temporary period going to end?

I guess that's the incentive for me to finally get sorted with moving my email elsewhere....

Re: Unknown Sender errors from Greenby

MisterW — Sun, 15 Mar 2026 14:12:45 GMT

@balvack2

It's not hosted by Plusnet: it's hosted / registered elsewhere with email forwarding

Sounds like your domain registar only provides a basic email forwarding service. If they provided a true hosting service then you'd be sending using their smtp servers.

It's really worrying that you say that it's only temporarily still working on my mail client. When is that temporary period going to end?

I dont have that detailed information. All I can say is that the plan was for all access, for both sending and receiving, to go via the Greenby proxy in order to make migration as transparent as possible for users. My understanding is that for technical reasons relay.plus.net is not currently routed via the proxy but will be, as soon as possible.

Re: Unknown Sender errors from Greenby

balvack2 — Sun, 15 Mar 2026 16:46:47 GMT

@MisterW

I've delved into my domain hosting setup and found that a long time ago I'd added this TXT entry to the DNS configuration. If I recall it was to permit outgoing (?) email to come from plusnet via my domain.

v=spf1 include:_spf-internal.plus.net include:_spf-internal2.plus.net include:secureserver.net -all

Would adding an additional record for whatever the Greenby equivalent is allow me to continue sending from my mail client as I do at present before relay.plus.net gets re-routed through the proxy?

Re: Unknown Sender errors from Greenby

MisterW — Sun, 15 Mar 2026 17:09:11 GMT

@balvack2

If I recall it was to permit outgoing (?) email to come from plusnet via my domain.

An SPF record doesnt actually permit sending of mail, it just means that mail received from your domain via those servers is to be treated as authorised.

Would adding an additional record for whatever the Greenby equivalent is allow me to continue sending from my mail client as I do at present before relay.plus.net gets re-routed through the proxy?

No. Most email providers will only allow mail to be sent from domains that are hosted by them. As I said earlier , the Plusnet servers had a loophole that would permit mail to be sent from any domain. The Greenby servers will only allow mail from domains that they actually host.

Re: Unknown Sender errors from Greenby

balvack2 — Sun, 15 Mar 2026 17:33:59 GMT

thanks for the clarification @MisterW

I set it up so long ago I couldn't remember why it was needed....

Re: Unknown Sender errors from Greenby

MisterW — Sun, 15 Mar 2026 17:39:14 GMT

@balvack2 if you've got as many as 10 mailboxes, then I'd look at Mythic Beasts for email hosting. You can have unlimited mailboxes, aliases subject to a total 2GB space on their mail only product. Some other hosts charge on a per mailbox rate so can work out expensive with many mailboxes.

Re: Unknown Sender errors from Greenby

balvack2 — Sun, 15 Mar 2026 18:21:38 GMT

Thanks @MisterW

I'd seen them recommended elsewhere so had already planned to contact them with the details of our 'idiosyncratic' configuration to see how best to move things forward.