It could happen sometimes that your IP is blacklisted by some email provider, or anti-spam services. If you receive an alert from the diagnosis tool, click on details to find the unblocking forms.
To check your Email deliverability, YunoHost provide some tests avilables in the Diagnosis tool. This tools evalutes a lot of configuration and ip reputation points. It gives you also an indicator if some mails are blocked inside the mail queue (waiting to be sent).
all the points evaluated by [the well known mail-tester.com](https://www.mail-tester.com) except for mail content (usefull if you prepare a newsletter).
YunoHost is only able to test generic blacklist using the DNS RBL mechanism. However, Gmail, Microsoft, Yahoo or Free maintains their own blacklisting mechanism, so in some situation you may need to contact their teams through dedicated forms or use dedicated tools.
- [Microsoft guide for postmaster](https://sendersupport.olc.protection.outlook.com/pm/)
- [Information about SMTP return code from Microsoft](https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx#Codes)
- Reputation Management tools :
- [Junk Email Reporting Program (JMRP)](https://postmaster.live.com/snds/JMRP.aspx)
- [Smart Network Data Services (SNDS)](https://postmaster.live.com/snds/index.aspx)
- [Get support form for deliverability issues](https://support.microsoft.com/supportrequestform/8ad563e3-288e-2a61-8122-3ba03d6b8d75) (Sadly you need a Microsoft account :/ )