Can I add TXT records to the PlusNet DNS?

[#1]

I have seen this question asked in the past with no real answer given.
I'm building my own mail server and would like to try and use SPF and DKIM, both of which require adding TXT records to the DNS.
Can I do this, even if it means raising a ticket to have them added through the back-end?
I realise the web screen only offers A, C and MX entries in its dropdown.
Please a definitive answer from PlusNet would be most appreciated.
Thanks.

[#2]

It's not possible I'm afraid. The functionality isn't built into our domain control system.

[#3]

That qualifies as a definitive answer, thanks Bob 
Would it be possible to manage the DNS elsewhere but have the mailbox hosting at PN still work?
I've got my MX configured so my own server is first and Plusnet's are second so that mail goes to the Plusnet mailbox if my server is offline. If I could set up the existing records on a DNS external to PlusNet where I can also configure TXT and other record types then I would be able to set up SPF and DKIM while still retaining the mailboxes for the domain at PN.
I guess there is nothing stopping me changing my domain registratrar's tools to change to use their DNS without changing anything at PN. But would it still be a "hosted domain" on PlusNet despite the domain's nameservers not being the Plusnet ones?
Can I do this ?

[#4]

FreeDNS / afraid.org offers free dns hosting / config and they allow many different types of records:

The service is free and I think you get up to five or ten subdomains BUT any user can attach to your domain and create their own subdomain on it. You can pay a fee and go stealth if you prefer not to let others use it.
http://freedns.afraid.org

[#5]

Quote from: starfry

Would it be possible to manage the DNS elsewhere but have the mailbox hosting at PN still work?

Officially, no.

Quote from: starfry

I've got my MX configured so my own server is first and Plusnet's are second so that mail goes to the Plusnet mailbox if my server is offline.

That's not really a supported set-up either if I'm honest. The intention has always been that if you're running your own mail server, you use the 'SMTP' option in the Member Centre. When you do this, the maildb entries for that domain are killed so local delivery to the Plusnet mailbox is no longer possible. Your domain is set up slightly unusually in that it's configured to deliver mail using POP3, however you've designated a higher priority MX record to point to your SMTP server.

Quote from: starfry

If I could set up the existing records on a DNS external to PlusNet where I can also configure TXT and other record types then I would be able to set up SPF and DKIM while still retaining the mailboxes for the domain at PN.

In theory that would work, however like the above, it's not a supported config and we've never intended for the system to be used (abused?) in this way.

Quote from: starfry

I guess there is nothing stopping me changing my domain registratrar's tools to change to use their DNS without changing anything at PN. But would it still be a "hosted domain" on PlusNet despite the domain's nameservers not being the Plusnet ones?

As above, you'd be doing this at your own risk. It could lead to problems and if support realise the situation it wouldn't surprise me if the zone records at our side were removed and the domain deleted from our systems.
Continuing to point web traffic at the CGI platform is fairly safe but anything else has a risk associated with it.