Sending multiple emails fails to Micorsoft 365 fails but works with GMAIL

[gwinterhalter]

With Office365 SMTP I am using the Send HTML example that sends the first email succesfully but all susbsequent emails fail with "Error, Status Code: 550, Error Code: -109, Reason: send body failedFree Heap: 199248" Upon reset the first message is successful

With the same sketch Google Gmail SMTP succeeds for all messages sent and when forwarded to my office365 email address the first one forwards and all subsequent fail to forward until reset.

1. Any thoughts to fix?
2. Is there any functions in library to logoff or disconnect SMTP service with this library?

[mobizt]

1. Any thoughts to fix?

The status code 550 is because the requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)

Please avoid sending Email too frequent and try delay the next message sending.

2. Is there any functions in library to logoff or disconnect SMTP service with this library?

The third parameter (bool closeSession) of function sendMail is for closing the session or sign out which the default value is true that means it will sign out when message sent if you leave this parameter default value by not providing third parameter to the function.

You also can close session later by calling smtp.closeSession().

[mobizt]

For the detail message of status code 550, please print this to see what SMTP server says after you get the SMTP server related error like in this case.

Serial.println(smtp.statusMessage());