I can send mails using an office 365 account (a@domain.com) with host as smtp.office365.com in my website. But if I set a different email (b@domain.com) for 'From' address I get the error,

Mailbox unavailable. The server response was: 5.7.60 SMTP; Client does not have permissions to send as this sender

I have given 'Send as' and 'Send on behalf of' permission for a@domain.com as follows but still not working.

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Both a@domain.com and b@domain.com are 'Exchange Online (Plan 1)' licensed accounts. What am I doing wrong? Thanks

  • 1
    At a first glance: you did nothing wrong. How long did you wait to try it? – Lenniey Feb 23 '18 at 11:25
  • @Lenniey thanks, it has been more than 24 hours – Asela Feb 23 '18 at 11:51
  • 1
    You say you "send from your website", can you send the mail as user b@domain.com if you use Outlook365 directly? – Lenniey Feb 23 '18 at 12:32
  • 1
    Why are you sending email this way? Inboxes are for users – Jacob Evans Feb 23 '18 at 22:12
  • @Lenniey yes I can send from both accounts directly from mail client – Asela Feb 27 '18 at 7:04

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