Email fails to deliver with apostrophe in address

David Ewer 26 Reputation points

I have a client who's email is hosted on Office365 and one user has reported that when they reply to a particular email it fails to deliver. The NDR reports the following error: SMTPSEND.Utf8RecipientAddress; UTF-8 recipient address not supported.

The email address that they are replying to contains an apostrophe and I wondered if this is significant. When my client replies to his customer he CCs in one of the customer's colleagues and this copy is delivered successfully.

As a test I created a test user on my own Office365 tenant and gave the test user an email address with an apostrophe. I emailed my client, which he received, and asked him to reply, which he did, but this also failed to deliver. The NDR reports the following: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup . When I sent an email to my test from another mailbox outside of Office365 the test delivered successfully.

The NDR my client receives when emailing his customer is as follows (I have changed server and user names for privacy): rejected your message to the following email addresses:
Gordon.O’ (Gordon.O’
The message couldn't be delivered because it contains characters that the recipient's email server doesn't recognize.
To fix this, set your email program to send messages using a different character set than UTF-8. In Outlook, for example, you can make this change in Options > Advanced > International options, then resend the message. If the problem continues, forward this message to your email admin.
For Email Admins
This issue occurred because the message was sent using the UTF-8 character set, which the receiving email system doesn't support. To fix this, the sender can try sending the message using a different, supported character set. Or if their mail server supports it, you can ask the recipient's email admin to configure their mail server to advertise support for SMTPUTF8, as specified in RFC 6531.
For more information, see Error code 5.1.17 in Exchange Online and Office 365. gave this error:
SMTPSEND.Utf8RecipientAddress; UTF-8 recipient address not supported.

Diagnostic information for administrators:
Generating server: CWLP123MB4452.GBRP123.PROD.OUTLOOK.COM
Remote Server returned '550 5.1.17 SMTPSEND.Utf8RecipientAddress; UTF-8 recipient address not supported.'

Can anybody suggest why this error is occuring?



Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Lucas Liu-MSFT 6,101 Reputation points

    Hi @David Ewer ,
    In order to better solve this issue, I want to confirm with you what the format of your test account is like. Is it as shown in the picture below? Accoridng to my test in my environment, I can successfully send an email to this email. If my settings are incorrect, please correct me in time.

    1.Please try to reply to emails containing apostrophe in OWA.

    2.Please send an email directly to this test mailbox containing apostrophe to see if it can be sent successfully.

    3.Please try to manually enter the email address and send an email. First, you can click "X" to clear the automatically complete email address.

    4.Accoridng to the error information from NDR, please following the path: Option -> Advanced -> Internnational options and select the “Automatically select encoding for outgoing messages”. Then try to send the email again.

    If the response is helpful, please click "Accept Answer" and upvote it.
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