Cannot Send Mail error message of not a valid email address

Cathy-0944 20 Reputation points
2026-08-19T20:16:41.1+00:00

I purchased my domain through Act Now Domains (who apparently has partnered with GoDaddy to support the accounts). A few years ago, they transferred the email functions to Microsoft. I am a sole proprietor business owner so I am both the Admin and the only individual on the account.

The mail account has been set up (as Microsoft Exchange) on my iPhone from the beginning and I had no problems until recently. Now when I try to email that account from another email account on my iPhone, it holds the message in the Outbox. When I attempt to resend it, I get the following message.

Cannot Send Mail

"my email address" is not a valid email address and has been rejected by the server. The message has been placed in your Outbox.

As I said, I have never had this problem before. I have tried multiple "troubleshooting" solutions, including deleting the mail account on my iPhone and adding it back in. Nothing works and finding help as the admin is next to impossible. I have been on a continuous loop with GoDaddy that is getting me nowhere. In the middle of a text conversation, they ask for me to validate the account, which I did more than five times. I have also sent them multiple test emails (per their request) but sending from that account is not the problem and after I do, they tell me they received it and that's where it stalls.

Has anyone encountered anything like this or have any ideas how to fix it? Thank you!

Microsoft 365 and Office | Subscription, account, billing | For business | Other
0 comments
Answer accepted by question author
Kai-L 19,060 Reputation points Microsoft External Staff Moderator
2026-08-24T22:51:08.2933333+00:00

Dear Cathy,

No need to apologise, the detail is genuinely helpful. I should be upfront that what you are describing does not look like a Microsoft 365 filtering problem. The "550 No Such User Here" rejection comes from the server that refuses the message, and that happens before the message ever reaches Microsoft. If Microsoft never received it, then blocked senders, quarantine, junk folders and mail flow rules cannot be the cause. That is also why nothing turned up in your spam folder. Your Exchange checks back that up. Your mailbox is listed, your name and business address are correct, and your domain shows as the only accepted domain. Everything on your side is configured as it should be.

The fact that every address you hold with that host produces the same 550 points to their platform still treating your domain as locally hosted, so it delivers internally instead of following your MX record to Microsoft 365. That would explain why their logs show the message as sent while nothing arrives.

Given how long this has gone on, it is worth opening a support case with Microsoft so an engineer can review your mail flow with you directly and confirm this in writing. Your message trace results will help them get there quickly. For guidance, see Get support - Microsoft 365 admin.

I hope this helps. Looking forward to your reply.

Was this answer helpful?

1 person found this answer helpful.
0 comments

8 additional answers

Sort by: Newest
Most helpful Newest Oldest
  1. Cathy-0944 20 Reputation points
    2026-08-22T16:34:52.5666667+00:00

    Well, after two days of hours-long chat sessions with my domain provider and my host provider, they are sending me back to Microsoft. Here is what was done and what they are saying.

    1. DNS settings - after much discussion, domain provider advised the DNS settings were wrong. They referred me to my host provider with specific language on how to fix it.
    2. Host provider - confirmed the DNS settings were changed and said it could take 4-6 hours to update. They also walked me through new settings for my email settings on iPhone. I won't bore you with the fiasco that occurred.
    3. Follow-up - yesterday I followed up as the email was still not routing to my business email with Microsoft Exchange. To make a very long story short, the host provider stated the DNS settings were correct, that the emails are processed on their end but the emails are not appearing in my Microsoft business email.
    4. Response - the host provider closed their review with the following: "Since [business email] is hosted on Microsoft 365/Outlook, could you please check whether [the sending email] has been added to any blocked senders list, spam filters, quarantine policies, or mail flow rules within your Microsoft 365 account? It's possible that messages from [sender email] are being filtered, blocked, or quarantined before they reach your inbox. I would also recommend checking your Junk Email and Quarantine folders, as well as any inbox rules that may automatically move or remove incoming messages. As we can see there is no issue from the server end. Eveyrthing [sic] is working fine from the server end. We can see the emails being sent from our side, so the next step would be to verify whether Microsoft 365 is preventing them from being delivered to your mailbox."

    What I discovered is any email I have (I have multiple for various blogs) with the Host provider gets the same SMTP (error 550) message when sending to my Microsoft business email. We only tested one of them (the one I originally wrote about here). Despite them assuring me they can see the server is working fine and sending them, on my end if I use that same email address, I still get the SMTP error but they insist their end shows it was sent.

    Can you help me with the part where the emails may be blocked by my Microsoft business email on your end? Where can I check to find that? And if it is, how do I fix it?

    P.S. Prior to this, I checked my spam folders and there were no messages there.

    Thank you. Sorry this is so long.

    Was this answer helpful?

  2. Cathy-0944 20 Reputation points
    2026-08-21T18:47:22.3833333+00:00

    Thank you. Just to make life interesting, another player has come into the picture - my web host. I got someone at GoDaddy who was helpful and told me the DNS needed to be changed by Hostgator (my web host). He ran a report and gave me what needed to be shared. Hostgator made the changes but when I tested it this morning, it is still noww working. So back to Hostgator. Sigh

    Was this answer helpful?

  3. Cathy-0944 20 Reputation points
    2026-08-20T13:39:21.38+00:00

    Thanks for this thorough response. I'm not sure how much my technically-challenged brain absorbed :-) but I gave it my best shot.. Some of the options in the admin center looked different but here is what I found.

    1. I had to click on other links, including an Exchange admin center. There the choices appear more consistent with what you describe. My business email is the only one listed.
    2. My name and my business email address are the only one listed.
    3. My business domain address is the only accepted domain shown.
    4. I'm not sure I did the message trace right but the failed message does not show at all on the report. The only exception is when I resent the message under my third mail account I have on the iPhone and that shows it delivered successfully.

    My next step will be going to GoDaddy/ActNow. I do not have a lot of hope there. They say they offer email, chat or text to contact them but when I started, I used email as it was so involved. Eventually my email came back saying it was an unmonitored email. Then I did text and was held captive in an endless loop of nonsense.

    Not your problem, I know. I am sooooo thankful for your help and guidance. Wish me luck!

    Was this answer helpful?

  4. Cathy-0944 20 Reputation points
    2026-08-20T01:13:58.2766667+00:00

    Thank you! I will test this out in the morning and let you know how it goes. It has been an exhausting day. :-)

    Was this answer helpful?

    0 comments

Your answer

Answers can be marked as 'Accepted' by the question author and 'Recommended' by moderators, which helps users know the answer solved the author's problem.