sending mail problems ...

Hi!

An error is received by the users requesting photos ...

De: Mail Delivery System <MAILER-DAEMON@gelf7.thinline.cz>

Enviado: domingo, 8 de octubre de 2023 23:26

Para: XX@gmail.com <XX@gmail.com>

Asunto: Undeliverable: Airplane-pictures.net photo feedback. Image ID 1520346

This is the mail system at host gelf7.thinline.cz.

I'm sorry to have to inform you that your message could not

be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can

delete your own text from the attached returned message.

The mail system

<XX@gmail.com>: host

gmail-smtp-in.l.google.com[2a00:1450:4025:402::1b] said: 550-5.7.26 This

mail has been blocked because the sender is unauthenticated. 550-5.7.26

Gmail requires all senders to authenticate with either SPF or DKIM.

550-5.7.26 550-5.7.26 Authentication results: 550-5.7.26 DKIM = did not

pass 550-5.7.26 SPF [outlook.com] with ip: [2a00:1ed0:2:0:1:5bef:c85d:1] =

did not 550-5.7.26 pass 550-5.7.26 550-5.7.26 To mitigate this issue,

please visit Gmail's authentication guide 550-5.7.26 for instructions on

setting up authentication: 550 5.7.26

https://support.google.com/mail/answer/81126#authentication

k8-20020aa7d8c8000000b00533ff29423csi3963949eds.161 - gsmtp (in reply to

end of DATA command)

Regards!