Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am struggling to find anything on the interweb,

We have a client and the email address we have been given for one of their employees contains 2 apostrophes.

One of our team is struggling to send an email to said employee. The client says the email is valid, but the postmaster reply tells me otherwise.

could not be delivered. The problem appears to be :
-- Recipient email address is possibly incorrect

Additional information follows :
-- 550 5.1.1 <xx.xx'xxx'>... User Unknown

Could anyone shed any light; is this a problem with the user being unknown or is the 2 apostrophes causing an issue.

EDIT: Is there any way to encode an apostrophe?


share|improve this question
What e-mail service are you using to send the e-mails? According to, apostrophes are valid characters in e-mail addresses (obviously); so your e-mail service must be the problem (not his, if he's already successfully receiving e-mails from others). Also, make sure you're not e-mailing from some kind of SQL database - apparently SQL turns bob.o' into bob.o\' – jrc03c Jul 13 '10 at 14:54
You might also try putting the entire e-mail address in quotes (such as "bob.o'"), or intentionally put the escape character before the apostrophe (such as bob.o\' – jrc03c Jul 13 '10 at 14:57
Are you sure the problem is the apostrophes? A "user unknown" error coming from the recipient domain's postmaster address suggests the address probably just misspelled somehow. Are other people on your team able to send e-mail to that address? Double check with them or with the recipient what the exact spelling of the e-mail address is. Or, if possible, have the other person send you an e-mail from that address and try replying to it to test that works. – Bavi_H Jul 14 '10 at 3:42
It is the email address the client keeps giving us, they use lotus notes, and this is supposedly the person's "external email" – Luke Duddridge Jul 14 '10 at 7:56

You have to send it as "email'with'apostrophe"

share|improve this answer
sorry didnt work – Luke Duddridge Jul 13 '10 at 15:43
Then it's just the wrong e-mail address. – BloodPhilia Jul 13 '10 at 15:53
I am starting to think that way. – Luke Duddridge Jul 14 '10 at 7:54

Please provide a bit more details -- what software/platform are you using to send email?, please provide more details about the undelivery message.

There is a tag marked "outlook" with your question, so I am guessing you are using Outlook.

I use Outlook 2007 and I am definitely not seeing this problem.

I just created a test account with username te'st'

I sent email from my work account (using Outlook 2007) to this test email address. I did not have to do anything special in Outlook. I just entered the address in the "to" field just as I normally do.

The email was received just fine.

share|improve this answer

A quick test using Java's new InternetAddress("bob.o'", "Bob O'Reilly", "UTF8") does not get me any special encoding at all:

Bob O'Reilly <bob.o'>

And indeed, using Apple Mail I can use such addresses with my own catch-all domain without any problems.

Update: also, using Apple Mail I can send to such address through an Exchange server. And I even logged in to work, and using Outlook 2007 I have no issues either.

What if you explicitly add the user to your Outlook's address book? Are you sure the single quotes did not somehow get converted into curly quotes? Or, another update: you can test using Gmail aliases, like your.account+what' Again, no trouble here.

share|improve this answer

Everyone here is wrong. There are 2 different forms of an apostrophe, the typographic ("smart") format and the typewriter ("dumb") format. Since different applications can type different formats, by default, it's a terrible idea to use an apostrophe as you are using, at best, a quasi-7-bit character. While there are workarounds there are going to be mail servers and apps that simply throw up on an apostrophe in varying formats and, again at best, the individual with an apostrophe in their mailto will find that they either can't send or receive mail successfully at a rate approaching those that don't use an apostrophe.

share|improve this answer
up vote 0 down vote accepted

Turned out email was invalid.

So got a different one to send to, this time without all the '

Dont get me wrong, emails with apostrophes are valid, just in this case they didn't equate to a real email.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.