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Testing SMTP Authentication using Telnet

Testing SMTP Authentication using Telnet

Testing SMTP Authentication using Telnet

SMTP authentication allows you to send email through our SMTP servers when you're not connected to our network e.g. when you're on holiday or when sending email from your smartphone. Without SMTP authentication you would *always* need to be connected via a Plusnet connection in order to send messages using our servers.
Plusnet allows customers to use SMTP authentication as long as they have a paid-for subscription account.
Your SMTP authentication credentials are either

  • the username and password you use to log into the Member Centre, or
  • a mailbox identifier of the form username+mailboxname with password for that mailboxname.

NB: You should *avoid* using secure authentication (SSL) or TLS as these features are not currently supported by our servers (although they will be in the future).
Using a mailbox identifier rather than account username is preferred from security considerations since the information is transmitted over an insecure connection.
If SMTP authentication isn't working for you then you can test it from a command line using a program called Telnet.
To do this, open a command prompt or terminal window and telnet to our SMTP server like this (note customers of vISPs other than Plusnet should amend the server address accordingly e.g. relay.force9.net if you're a Force9 customer, relay.free-online.net for Free Online):
C:\Documents and Settings\bpullen>telnet relay.plus.net 25

You should see something like this returned:
220 relay.plus.net ESMTP Exim Wed, 10 Mar 2010 12:58:17 +0000

If that doesn't connect it is possible your mobile service provider is blocking use of port 25. In this case try again replacing '25' by '587'.
Next type the following and press Enter:
ehlo relay

You should see something like this:
250-relay03.plus.net Hello relay [80.229.xxx.xxx]
250-SIZE 104857600
250-PIPELINING
250-AUTH PLAIN LOGIN
250 HELP

Next type:
auth login

You'll receive a response like this:
334 VXNlcm5hbWU6

You now need to enter your account username and password (the ones you use to log into our website), or mailbox identifier and its password (see above) but before you go ahead and do this you'll need to convert both the username and password into 'BASE64' format. This is easy to do using an online conversion tool like the one here. Simply enter your username or password and then press the 'Encode' button.
Now you've converted your login details let's enter the username in reply to the 334 response we've just received:
dXNlcm5hbWU=

You should get another 334 response:
334 UGFzc3dvcmQ6

Next enter your encoded password:
cGFzc3dvcmQ=

All being well you should get a 235 response as follows:
235 Authentication succeeded

If you receive a '535 Incorrect authentication data' response instead then there might be a problem with your account and you should raise a support ticket using the Help Assistant on our website.
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