Email functionality overall is working fine.

However, if a Share request is initiated (one that requires moderation) that specific email will not come through, throwing:

Failed attempt 1 sending mail to recipients: access.requests@domain. Mail Subject: Tiago Duarte wants to share 'blah-blah' with Crazy Johnny. Error: SmtpException while sending email: System.Net.Mail.SmtpException: Mailbox unavailable. The server response was: 5.7.1 Client does not have permissions to send as this sender at System.Net.Mail.DataStopCommand.CheckResponse(SmtpStatusCode statusCode, String serverResponse) at System.Net.Mail.DataStopCommand.Send(SmtpConnection conn) at System.Net.ClosableStream.Close() at System.Net.Mail.SmtpClient.Send(MailMessage message) at Microsoft.SharePoint.Email.SPSmtpClient.Send(MailMessage msg) at Microsoft.SharePoint.Email.SPSmtpClient.TrySend(MailMessage msg)

The email from the Send an email invitation checkbox is sent perfectly. Grant or decline actions emails are also sent.

Note: This has been working fine for over a year until last week.

Attempts: tried multiple outbound from addresses, but it doesn't seem to even matter, always throwing the same exception

Similar issue:


1 Answer 1


This is due to SharePoint impersonating users when sending invitation emails, typically. The Exchange Receive Connector often will not allow it by default. Generally one should set up an Exchange Receive connector with Externally Secured and IP restricted to the SharePoint servers in the farm to work around this issue.

  • I've read that you can assign "send as" permissions, like in the "similar issue" above. kind of frustrated as to why this only became a problem now and not before. Jul 6, 2017 at 15:02
  • Send As won't work unless you're passing mail through an SMTP relay that is capable of authenticating (e.g. like an IIS SMTP relay). This is not required, though.
    – user6024
    Jul 6, 2017 at 15:03
  • looks like the outgoing smtp server changed recently. changing back to the previous server fixed the issue. anyway, the new server will need to be configured properly as you stated in your answer Jul 10, 2017 at 13:14

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