Office365 throttling inbound messages S77719

Copper Contributor

We have an onprem exchange server. Recently changed public IP's and now MS is throttling our emails to recipients who are on office365/


The error is S77719, 451 4.7.500 Server busy. Please try again later.


Yahoo was doing something similar and we had them fix it. We are a business, not a marketing firm, we send transactional emails and regular email.


Is there anything else we can do to speed up MS to permit our emails? I've also signed up for their Junk mail program and sent a follow up to MS deliverability support earlier this AM without any response. 

2 Replies
Best open a support case.

@Vasil Michev which I did and it took 3 replies to get the different analysts to understand the request and they repeatedly stated my IP was not eligible for immediate mitigation! They were sending cookie cutter template responses, clearly not reading my emails entirely. Sometime overnight the messages cleared the queue and sending clean again without changing any formatting.


FWIW, here's their response:


Mail Formatting and user management


User/Subscription Management:

·        Ensure you keep mailing lists up to date. Consider having inactive users confirm their subscription and remove them if inactive for certain period of time.


·        If you enroll in JMRP, consider removing users who mark your mail as unwanted. This helps keep your email lists populated with only interested users.


·        Ensure that the unsubscribe process is visible and that you respond to requests to remove a user from your mailing list in a timely fashion.


·        To ensure interested recipients are receiving mail in their inbox, encourage users to add you as a contact or as a safe sender in their options.


·        Many senders include a statement like the following in their welcome mail when user subscribe: To ensure delivery to your inbox, please add to your address book.


Mail formatting:

o   Clearly mark your emails so that Windows Live customers are able to quickly and easily identify that they requested emails from your service.


o   Avoid urgent calls to action in email notifications, invites or advertisements such as "Must sign up today!" "Log in right now!"  "Update immediately!" since these are common tactic used by malicious senders.


o   If you have enrolled in JMRP and are seeing feedback on certain types of mail messages:


§  Consider giving user's more control over the volume and types of mails they receive. For example, allow them to configure mail frequency: daily, weekly, etc. and opt-in to the types of mail messages they are interested in receiving: daily offers, sales only, gift reminders, holidays only and so forth. 


§  If you receive complaints about your legitimate emails then there is something about these emails that customers do not like or find suspicious.  You should evaluate the complaints and adjust your emails to address those issues.


While there are no guarantees of improvement, most senders find that structuring emails to address the complaints in JMRP has a beneficial effect on deliverability.


In addition, if you haven't already done so I encourage you to sign up for the two free programs we recommended:  the Junk Mail Reporting Program (JMRP) and the Smart Network Data Services program (SNDS).  Actively using the information these programs provide can help you identify and monitor issues that can impact sending reputation.


·        Junk Mail Reporting Program (JMRP) - As we noted before, your recipients are the best indicator that the email you are sending is wanted.  This helpful feedback mechanism allows you to ensure that mails being sent from your IP are not resulting in negative feedback from your users. Enroll at


·        Smart Network Data Services program (SNDS) - The SNDS program provides data about traffic seen originating from your registered IP, such as mail volume and complaint rates. For more information about this free program refer to To register, please go to (Reminder: As part of the enrollment process, you are asked to sign the JMRP program agreement and then send a response to Support indicating that it has been signed.  It's not uncommon for that step in the enrollment process to be missed.)


If you have a deliverability issue in the future, we encourage you to file a new ticket to have your issue investigated. We have streamlined and improved the Deliverability Support process by implementing an automated system the reviews your sending IP(s) and responds with a Deliverability Report which provides a status on each IP submitted.


This system is able to automatically mitigate many deliverability issues. If your issue can't be automatically mitigated or the system can't take action, the Deliverability Report includes a link you can use to submit additional information so that our 24 x 7 Deliverability Support team can investigate and respond to you. For your reference, the link to report an issue is