I changed email smtp services. I was using gMail but switch to dotnetmailer.

Every now and then I get a message that says: Mailbox unavailable. The server response was: Requested action not taken: mailbox unavailable.

What mailbox is that referring to and what can I do about it?

thanks.

That's coming from your provider and you need to check with them.

Most likely you're hitting email volume limits and they're blocking you from sending too many emails in a short time. Most regular ISPs have limits on how much email you can send through an account in a given timeframe and that's what that message sounds like.

If you're doing high volume sending you probably need to look into an email server specific solution like Mailgun (which is what I use for the message board, store and samples), SendGrid and the like.

Most of these services provide plain SMTP services so you can use existing SMTP email code, or they provide custom APIs to send messages through including APIs where you basically provide a message and list of email addresses and they handle the actual sending of the emails (ie. you're not looping through your senders one at a time). For large lists this is the way to go.

Most have free plans for a certain number of emails. I've never come close to the free limits, but that depends on what you're doing.

+++ Rick ---