Changes coming to the SMTP Authenticated Submission client protocol

The_Exchange_TeamI'm starting to hit the sender thread limit exceeded problem sometimes. Our platform sends out emails to notify when services are down.

We are currently using SMTP Authenticated Submission. If we switch to sending emails using Modern Auth, will the 3-simultaneous thread limit still apply?

The_Exchange_Team I would also like a way of turning this feature off, our customer service team is finding it hard to filter through our dispatch emails to find emails they have written, and automated rules don't work on the sent items folder very well.

The_Exchange_Team 

is there a way to deactivate "Sent email will now be stored in the Sent Items folder of the mailbox." for a mailbox?

This behaviour is not GDPR comliant in our use case.

We recently migrated from local Exchange to O365. We have some console apps that periodically check for and send out queued emails in batches. 

We discovered that if we didn't throttle the send rate in the smtp loop, the O365 account used to authenticate with our tenant would start getting 5.2.0 connection errors "STOREDRV.Submission.Exception:SubmissionQuotaExceededException".  We put in a 3-second delay which would throttle the emails to 20/minute, which seems to work OK (I believe the rate limit is still 30/minute?).

Recently one of our apps ran without the delay, and the user account used to send emails started getting blocked. We disabled the process and added back in the delay, but we're still unable to connect with that user (changing the SMTP authentication to a different user worked fine).

My question is, how long does the block stay on the account? an hour? 3 hours? 24 hours?

To do this, it leverages the decoupling between the SMTP envelope and data. It connects to smtp.office365.com:587 and issue 3 send-email transactions. Each transaction includes ONLY 1 of the recipients in the "RCPT TO" command. The data field contains identical headers across all 3 email are identical. In the example above, they all contain the 2 email addresses 'To' header and the 1 email address in the 'Cc' header. However, the message body will include a unique image URL.

This application has worked flawlessly over the past 3+ years allowing us to implement fine-grained email-open tracking.

However, over the past few days, there seems to be a change email where multiple emails are being delivered by Exchange. Each recipient in the email is getting the email where their email address is in the RCPT command AND every email for all other recipients as well! It appears as though Exchange is delivering emails to every email address mentioned in the RCPT command AND in the To and CC headers.

Consider the following SMTP transcript:

---------------------------begin------------------

MAIL FROM: sender@example.com

RCPT TO: user1@example.com

DATA

To: user1@example.com

Cc: user2@example.com

Subject: test email

test 1

.

MAIL FROM: sender@example.com

RCPT TO: user2@example.com

DATA

To: user1@example.com

Cc: user2@example.com

Subject: test email

test 2

.

---------------------------end------------------

I would expect user1 to receive 1 email with the text 'test 1' in the body and user2 to receive 1 email with text 'test2' in the body.

Instead, user1 receives 2 emails ('test 1' and 'test 2') and user2 receives the same 2 emails!

This doesn't seem correct. Is it a side-effect of this change? Any way to restore the correct behavior?

@Infiltrator There is no wait time of any significance. If you are not sending at the same time, you have nothing to worry about.