We received email "Undelivered Mail Returned to Sender"

Within these few days, when we sent email to guest with "@guest.booking.com", we received email (there are many of these emails) below just one example:


from:    Mail Delivery System <***>
to:    [our email removed]
date:    Mar 7, 2021, 11:08 PM
subject:    [Booking.com] Undelivered Mail Returned to Sender
mailed-by:    ***.booking.com

This is the mail system at host mailrouter-208.lhr4.prod.booking.com.

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

<our guested email removed>: host intercommail.booking.com[]
    said: 530 5.7.0 Must issue a STARTTLS command first (in reply to MAIL FROM

BrookAve 3 years ago



You cannot message a guest after they leave when its more than 7 days from check out date.

AirXpress Grou… 3 years ago

Thanks @BrookAve - yes we understand that after guest checked out we cannot contact to them.

but the my problem is happening when guest is not yet check-in and during staying time. We do have problem just within last few days only.

BrookAve 3 years ago


 ok thats weird, please report it to partner support asap, they will never see anything you post on here.


 Message or Call BdC PartnerSupport ***


  1. In the extranet, go to the ‘Inbox’ tab.
  2. Select ‘Booking.com messages’.
  3. Right Pane - Click on ‘See Contact Options’
  4. Choose Account
  5. Now choose Other
  6. Then at bottom , See all contact options, and click Message or Call
  7. As there is no one number for all partners, the number for your nearest BdC Partner Support is then revealed.


*** public main lines via Where you can reach us



how to contact partner support via private assigned number in inbox



Kind Regards