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phpmailer mailbox unavailable

APD Toronto
APD Toronto asked
Hi Experts,

I am using PHP Mailer and I am getting the following error. I think it has something to do with the mailbox not being on the same server, or some settings. I have had this issue before, but dont remember how I fixed it.

Mailer Error: SMTP Error: The following recipients failed: jsmith@smith.ca: Requested action not taken: mailbox unavailable or not local.
Watch Question

Fractional CTO
Distinguished Expert 2019
There can be several reasons.

1) jsmith@smith.ca really no longer exists.

2) Sending MTA has incorrect SPF/DKIM/DMARC settings, where all or some mail from sending domain is blocked.

3) Sending MTA is blacklisted either globally or internally with receiving MTA.

4) Sending MTA is misconfigured.

5) Sending MTA has port 25 outgoing connections blocked.

Likely others. The above are just what came to mind.

Use a tester like https://dkimvalidator.com, if you're sending mail from your own MTA (no relay like MailGun) for a quick analysis of your MTA config.

Note: I just picked https://dkimvalidator.com out of many testers like this. Best to try a few testers to determine which one works best.

Use a tester like https://mxtoolbox.com/blacklists.aspx to test if your domain is blacklisted.
APD TorontoSoftware Developer


I am sorry, but I was waiting for my client to open a mailbox for me to test. I will reopen this once I am ready.

In the meanwhile what is MTA?
David FavorFractional CTO
Distinguished Expert 2019

MTA (Mail Transfer Agent) like Sendmail or EXIM or PostFix. Some SMTP server code which initiates sending email.