Error 550 Relay Not Allowed

[#1]

My parents have no connection with plusnet other than  to have a mailbox each on my plusnet hosted domain which they access over a Vodaphone 3G dongle using authenticated SMTP with my plusnet user name and password. My son has his own paid for plusnet account but uses a mailbox on my domain and accesses that on his iPhone using my plusnet user name and password.
So if you have a paid for account and your partner has a payg account your partner should be able to access authenticated SMTP using your f9 user name and password.
Having explained that I hope that I am not breaking the rules and this gets switched off 

[#2]

Quote from: madjbright

Having explained that I hope that I am not breaking the rules and this gets switched off

I'd never really suggest giving your username and password to a third party, but we're not going to switch this functionality off or frown upon how you're using your account (unless shed-loads of spam starts originating from it of course!) 

[#3]

I have been trying to send PlusNet email via Outlook when away from home for some time, so thanks to James and Chris for explaining about authenticated SMTP.  It might be useful to include this information in the PlusNet FAQs, which are currently misleading on the issue; in fact they specifically say that it can't be done.  'Common Email Questions' No 7 at https://portal.plus.net/support/email/common_questions.shtml#access says:
"Important Note: If you are connecting to the Internet from a different location, you won't be able to use the PlusNet outgoing server. Instead you will need to send your emails using the outgoing server provided by the ISP on which you are connecting. "
Is authenticated SMTP supposed to be a secret?

[#4]

Right now, the authenticated SMTP service is an unsupported feature. It's as a result of a product we used to sell, but was opened up for subscription products.

[#5]

Quote from: puddy

It will not work with a payg account

Have just done it over GPRS with a Vodafone PAYG account.  Can send email using authenticated SMTP
Can also get emails using IMAP (or POP3).

[#6]

I'm surprised to read that authenticated access is not a supported feature as it was requested by a number of customers some time ago and was allocated an official suggestion number.  I've been using the feature for a long time now when I go abroad and it works a treat.

[#7]

@Saturn, I suspect the main reason we haven't plastered it all over our sales pages as a supported feature is the fact that it has a tendency to attract spammers looking to get hold of accounts that they can spam with.

[#8]

Bob
Sounds reasonable, but to me it is an invaluable facility.  I hope no one considers turning it off.  It would only be a risk if someone's username and password were discovered and then that person would have a whole bunch of trouble with their account. 

[#9]

It's the lengths would-be spammers go to on order to create accounts for these purposes that's the main concern.