Trouble receiving email from booking.com

Support General Configuration
1

For some reason I’m unable to receive email from booking.com, I seemingly have no issues with anyone else. I’ve included a verbose log of the transaction below. As far as I can tell Booking connects but doesn’t even try to transmit a message. This has been going on for a while (over a year). Booking support has been of no help. They are a major service so I don’t think this is some systemic problem on their end. My Gmail can receive email from them just fine. I have whitelisted booking.com although I see no indication that this is a spam issue. Any ideas?

2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040733: [172.18.0.5:25] connection accepted from [2.56.188.250:8000]
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040733: >> 220 mail Axigen ESMTP ready
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040733: >> 421 mail remote peer has closed connection
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040733: closing session from [2.56.188.250]
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: [172.18.0.5:25] connection accepted from [2.56.188.250:8004]
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 220 mail Axigen ESMTP ready
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: << EHLO WK7-4
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Set max data size to 102400 KB
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Set max received headers to 30
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Maximum recipient count set to 1000
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Wait for processing response at least 10 seconds
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: STARTTLS extension allowed
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: 8BIT MIME accepted
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: BINARY DATA extension allowed
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: PIPELINING extension allowed
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Set local delivery to all
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: DSN extension denied
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Greylist disabled
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: Set remote delivery to auth
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-mail Axigen ESMTP hello
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-PIPELINING
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-AUTH PLAIN LOGIN CRAM-MD5 DIGEST-MD5 GSSAPI
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-AUTH=PLAIN LOGIN CRAM-MD5 DIGEST-MD5 GSSAPI
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-8BITMIME
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-BINARYMIME
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-CHUNKING
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-SIZE 104857600
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-STARTTLS
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250-HELP
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 250 OK
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: << QUIT
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 221-mail Axigen ESMTP is closing connection
2025-08-12 09:45:08 -0400 16 mail SMTP-IN:00040734: >> 221 Good bye
2025-08-12 09:45:08 -0400 08 mail SMTP-IN:00040734: closing session from [2.56.188.250:8004]
2

Hello,

Both above SMTP-IN sessions are not from booking.com but from wk7-4.hetrixtools.com (resolved with 2.56.188.250).

$ host 2.56.188.250
250.188.56.2.in-addr.arpa domain name pointer wk7-4.hetrixtools.com.

$ host wk7-4.hetrixtools.com
wk7-4.hetrixtools.com has address 2.56.188.250
wk7-4.hetrixtools.com has IPv6 address 2a0b:f302:2:c::2

HTH,
Ioan

3

Ah you’re right. I do have Hetrix monitoring on this system. When I did a who.is on the IP address it was registered in Amsterdam, which is where Booking.com is based out of, so I incorrectly assumed that was the incoming request. I’ve since paused the Hetrix monitoring and tried to get Booking to send a couple verification emails but I see nothing on my end. So I don’t know what’s going on with them. But I don’t have an issue with anyone else sending to me and Gmail doesn’t have an issue receiving Booking emails :man_shrugging:

Only thing I can think of is Booking is seeing that my destination IP address is a dynamic residential address and preemptively not sending the email. Never had something like that happen before, however.