Prolateral Consulting Ltd
Prolateral Consulting Ltd

Because of a host of different email servers and clients it is easy to have a problem with configuring email or an SMTP host. This article covers the top five issues most people have with SMTP configurations.


Incorrect Username or Password

Many problems start by accidentally typing in the wrong username or password, or by copying and pasting it. Depending on your email client you might see a dialog box or pop-up box asking you to enter your username and/or password.  Entering it incorrectly can cause sending mails to fail.  Copying and Pasting can often be equally as problematic because sometimes during the selection for copy it adds either a leading or trailing space.

On some systems and servers the username and/or password can be case sensitive so always keep an eye on the case and the caps lock key.  Sometimes it is very difficult to decipher password that have a zero verses a letter 'o' or 'O' and the same for letters like 'i' and 'l'. If in doubt try pasting the password into an application like MS Notepad or something that displays mono-spaced fonts to see if that helps.

Of course it is also possible you are entering the wrong password altogether in which case you will need to reset it.  On the odd occasion you may just need to simply re-type your username and password even if it did work but now doesn't as sometime the password stores can become corrupt.

Server Not Found

First thing to check are you online? Can you surf the Internet and get to your favorite web pages without any problems.  If you can surf ok, then check your ISP and DNS settings are still okay and valid. If  you have changed any of your domain settings or records then you may have to wait for DNS to fully propagate.

More and more ISP's (Internet Service Provider's) are blocking tcp port 25.  TCP Port 25 is the standard port for outgoing emails but can often be blocked or get redirected by the ISP.  outMail is an outgoing SMTP service that supports alternative TCP Ports for sending emails to overcome this problem.  If it is blocked then it's an easy configuration change to use an alternative SMTP port.  More information and "How To" guides on individual servers and email clients can be found in the support section at (

Relaying Denied

The dreaded SMTP 550 Relay denied error message.  Basically the SMTP server is stating it can't accept your email for delivery.  There are many reasons for an SMTP 550 message, the more common one's are your ISP is blocking and preventing you sending emails using your own domain name.  (I.e you can send emails using the from address of This email address is being protected from spambots. You need JavaScript enabled to view it. but not from This email address is being protected from spambots. You need JavaScript enabled to view it.). Another common cause for relaying denied is you have the wrong username and password on the SMTP Authentication settings.

A further cause of the SMTP 550 error is you have changed networks.  A good example of this is you are at home or the office and your laptop and/or mobile device is sending emails no problems at all.  You then go out for a meeting and get connected to the local WiFi only to find you can't send emails anymore.  This is because your ISP only accepts connections to their SMTP server from within their network.  An annoying and temporary solution would be to change your SMTP outgoing server settings to match that of the SMTP server on the new local network or new ISP, assuming you can find that information, only to have to change it all back when you return home or to the office.

The SMTP 550 error was the main driving force for Prolateral to offer the outMail service. outMail is an SMTP Authenticated service that works from any location, any ISP and any email address, with alternative TCP ports as well.

Mailbox Full / Quota Exceeded

This is often a problem when you are trying to send an email to someone whose mailbox/inbox is full or over quota. These style of errors are typically not fatal one's because the email will stay on the outbound queue and retry.  The SMTP Error message for this is normally a 450 error.

Please don't get confused with your send quota compared to the recipients mailbox quota. A recipient's administrator may have setup quota's on the users mailbox for whatever reason and this will normally generate a retry error or an SMTP 450 error.  With outMail you have a quota limit on the number of messages you can send and not the mailbox storage size.  With an outMail exceeded quota message this is normally a permanent error with no retry and can be seen with an SMTP 554 Error.

No Such Address

In layman's term you got the recipients email address wrong or as mentioned above there may have been some domain settings or record changes that could cause this error.  Please note this error is typically not a configuration error on the server or client setup.  Check you have the correct address and try again.


About Prolateral

Prolateral Consulting is in business to put your organisation back in control of your own Information Technology, specialising in information and messaging security, computer forensic services, and disaster recovery planning.

Contact Info

Prolateral Consulting Ltd
Luton, Bedfordshire, UK
Tel : +44 (0) 8450 763760
Email : This email address is being protected from spambots. You need JavaScript enabled to view it.

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