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Using Outlook, I'm getting delivery errors saying that what I believe to be a valid email address is incorrect.


Sometimes when you send an email to a familiar address that you've used before, it can be rejected because of an apparent header syntax error.  For example, the bounce notification message may include a diagnostic like this:

Delivery has failed to these recipients or groups:

'' ( A problem occurred during the delivery of this message to this e-mail address.  Try sending this message again.  If the problem continues, please contact your helpdesk.

Further down the message you should see diagnostics like this:

Your message header syntax is not valid, please check sender and recipient 550 addresses.

If you read further down the message you should see the original headers showing the incorrectly-formatted addresses in the To: header.

Email address formats

An email address (in a message header) should show the recipient's real name first, (possibly enclosed in quotes) followed after a space by the actual email address in angle brackets. You can also omit the real name altogether, for example just give the actual email address by itself. There must not be any quote marks surrounding the email address. Below are shown some examples of correctly-formatted and incorrectly-formatted email addresses (all the examples use but you can imagine them as

Correct address examples:

Examples of correct email addresses

Incorrect address examples:

Examples of incorrect email addresses

Why are the addresses sometimes wrongly formatted?

There may be several reasons for the incorrect address formatting.  It may be due to an incorrect address entry in your Contacts.  More likely, it's been changed by the Exchange system.

Exchange doesn't create its own Internet mail headers: instead, it has a gateway that translates Internet headers to Exchange headers, and vice versa. An indication of this is a series of semi-colons separating the recipients:  internet headers always use commas to separate email addresses.

Also, in the apparent email headers, what you see is a list of what Exchange thinks are the recipient's names. For external recipients (that is, those outside the Sussex Exchange mail system), there is often no real name attached to their email address, but the Exchange system has - rather stupidly - populated what should be the "name" part with the email address. Sometimes, it seems, this happens even when there is already a name. And, sometimes it seems to happen more than once.

What we should see, is a To: header formatted like this:

Syntax of a To: internet mail header
So, the address is put in angled brackets alongside the name. The name is optional, and if omitted, then the angled brackets can also be omitted. Complicated names can be put in double quotes, as shown above.

What you can do

When you set up addresses in an Outlook contact group or distribution list, you need to make sure that only the person's real name is given in the Real Name box, and only their email address is given in the Email Address box. Don't enclose either in quote marks of any kind.

When composing a new message, follow the instructions below for the version of Outlook you are using:


  1. When you've entered the address in your To: box in Outlook 2013, click in one of the other boxes and then the To: box again until the address in the To: box appears underlined:

  2. Float your mouse pointer over the address, and the following dialogue box should appear.  Click on the Open Contact Card arrowhead as indicated in the image below:

    Outlook 2013 add contact via To box

  3. A Contact Card dialogue box should appear. Click on Add as indicated in the image below:

    Outlook 2013 contact card

  4. In the contact card editor, replace the email address in the Name box with the person's full name, or some other label if the email address is not that of a person:

    Outlook 2013 contact edit

    For example:
    Outlook 2013 contact edit

  5. Click OK.   You may be shown the following dialogue box:

    Outlook 2013 contact edit

    Make any further changes as required, then click OK.
  6. Click on Save to save the new contact:

    Outlook 2013 contact save

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This is question number 2478, which appears in the following categories:

Created by Andy Clews on 15 March 2012 and last updated by Alexander Butler on 14 March 2018