使用Microsoft 365通讯组列表时向Gmail账户间歇性投递失败问题求助

大家好，我遇到一个困扰快一年的问题，想请教各位帮忙排查：

• 我们组织的Microsoft 365通讯组列表，当外部邮件联系人（比如我自己的个人MS 365租户账户，或是Gmail用户）向列表发邮件时，会间歇性出现邮件无法投递到列表中所有Gmail地址的情况——完全摸不着规律，有时候正常发送，有时候就失败。
• 发件人会在发送邮件后的2-3天收到退信通知，而且只有外部域名的收件人会遇到这个问题，我们组织内部域名的用户接收完全正常。
• 这个问题不是单个通讯组的特例，在我们多个通讯组列表上都出现过类似情况。

以下是退信通知的示例（已修改隐私相关的邮箱地址）：

Delivery has failed to these recipients or groups:
dahonig22@gmail.com Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their email system isn't accepting connection requests from your email system. Give them the error details shown below. It's likely that the recipient's email admin is the only one who can fix this problem.

Diagnostic information for administrators:
Generating server: PH0P221MB0733.NAMP221.PROD.OUTLOOK.COM
Receiving server: PH0P221MB0733.NAMP221.PROD.OUTLOOK.COM Total retry attempts: 14

dahonig22@gmail.com 1/21/2023 3:45:51 AM - Server at PH0P221MB0733.NAMP221.PROD.OUTLOOK.COM returned '550 5.4.300 Message expired -> 421 4.4.2 Connection dropped due to SocketError'
1/21/2023 3:39:02 AM - Server at gmail-smtp-in.l.google.com (142.250.27.27) returned '421 4.4.2 Connection dropped due to SocketError'

这个问题已经持续将近一年了，试过一些常规排查但没找到根源，有没有大佬能给一些排查方向或者解决建议？非常感谢！

备注：内容来源于stack exchange，提问作者Brie