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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(163.2, 63%, 25%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EJP%3C/text%3E%3C/svg%3E)
Hello,
Please i need your help on this issue.
Recipient: ******@XXXX.com Sender: @XXX.XXX ServerIP: 52.98.178.242 Server: smtp.office365.com Header: Header size exceeds fixed maximum size Server response: 552-5.3.4 01JKSPHRJ9S1T5MSZZV6K09BBA ([@zendesk.com]): Rejected with MX smtp.office365.com - 552 Header size exceeds fixed maximum size The same happened to the recipient: ******@XXXX.com, ******@XXX.XXX, ******@XXXX.com
As the email is being sent from your custom email address: ******@XXX.XXX using your external email server, I will recommend reviewing what limits in attachments your server and end users have to avoid the rejections.
You are probably adding too many hops to the message flow. Or too many custom headers etc...
You cant raise the header size, instead troubleshoot it from the mail flow side and look to reduce the hops or whatever is filling up that header.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(166.4, 9%, 26%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ETC%3C/text%3E%3C/svg%3E)
I agree with Andy David's idea. Raising the header size limit is not supported at this time. Consider reducing the number of recipients and sending them in groups. Simplify the email subject or remove non-essential information from the header.
Is there any update on this thread? If the issue has been resolved, please mark the helpful replies as answers, this will make answer searching in the forum easier and be beneficial to other community members as well. Thanks for your understanding.