Gmail consistently sending mailbox.org emails to Spam despite SPF/DKIM/DMARC passing
Emails sent from my email are consistently being classified as spam by Gmail.
I tested delivery to two separate Gmail accounts and both messages were placed in Spam. A plain text message with no attachment and a separate message with an attachment were both affected. Delivery to Proton Mail succeeded normally.
Gmail reports SPF: PASS, DKIM: PASS and DMARC: PASS. The messages were delivered via mailbox.org outbound server
Gmail’s reason is: “This message is similar to messages that were identified as spam in the past.”
Has anyone else had this? This is a significant issue for me because I need reliable delivery to Gmail recipients for my work emails correspondence. If mailbox.org can't resolve the deliverability problem, I unfortunately need to move to another provider. I really want to stay with Mailbox.org as I love it so far but this is a crucial problem for me.
The same problem 
My Dad just confirmed my email went to his spam too on Gmail arghhhh
My Dad just confirmed my email went to his spam too on Gmail arghhhh
I notice it too. Seems a way of Google-Gmail deliberately bothering / discouraging other email providers. After all, nothing is wrong with the email itself. Still i hope something can be done about it.
So far i really do like mailbox.org.. !
d.
I notice it too. Seems a way of Google-Gmail deliberately bothering / discouraging other email providers. After all, nothing is wrong with the email itself. Still i hope something can be done about it.
So far i really do like mailbox.org.. !
d.
I recently experienced the same: two emails not being delivered to the correct GMail inbox. Only an acquaintance, so I did not ask about spam...
On the other hand, my plan is anyway to block incoming emails from GMail, as all my answers will be monitored by Google for ads and AI training. I just need to get my mother off from her old GMail account :-)
I recently experienced the same: two emails not being delivered to the correct GMail inbox. Only an acquaintance, so I did not ask about spam...
On the other hand, my plan is anyway to block incoming emails from GMail, as all my answers will be monitored by Google for ads and AI training. I just need to get my mother off from her old GMail account :-)
Seems like the same issue reported here:
https://userforum-en.mailbox.org/topic/5393-messages-are-not-being-received-or-sent-to-spam-folder
Seems like the same issue reported here:
https://userforum-en.mailbox.org/topic/5393-messages-are-not-being-received-or-sent-to-spam-folder
Hi,
Looks like one of the things that Google recommends to prevent valid emails from going to Spam is to add the email address of the sender to Google Contacts. I know this may not be possible in every single scenario, but you may try asking the recipient to add the Mailbox.org address to their Google Contacts before you send them the email. That may be a valid workaround in some cases.
I found this link which also suggest a few additional steps https://support.google.com/mail/answer/1366858
I hope that helps.
Regards,
Fred.
Hi,
Looks like one of the things that Google recommends to prevent valid emails from going to Spam is to add the email address of the sender to Google Contacts. I know this may not be possible in every single scenario, but you may try asking the recipient to add the Mailbox.org address to their Google Contacts before you send them the email. That may be a valid workaround in some cases.
I found this link which also suggest a few additional steps https://support.google.com/mail/answer/1366858
I hope that helps.
Regards,
Fred.
Hello,
Can we please have an answer to this issue? I have just joined mailbox with the intention of using it for business purposes, and noticed that I was not receiving replies from potential clients. I ran a test with different providers- proton mail and hotmail/outlook successfully delivered, while 3 out of 4 Gmail accounts sent the email to spam.
Please provide some support- I would like to stay with Mailbox if possible but as I can’t see any clear resolution to this, so will likely have to seek an alternative.
Thank you.
Hello,
Can we please have an answer to this issue? I have just joined mailbox with the intention of using it for business purposes, and noticed that I was not receiving replies from potential clients. I ran a test with different providers- proton mail and hotmail/outlook successfully delivered, while 3 out of 4 Gmail accounts sent the email to spam.
Please provide some support- I would like to stay with Mailbox if possible but as I can’t see any clear resolution to this, so will likely have to seek an alternative.
Thank you.
EDIT: this is probably my own fault.
My problem is similar. I could not even send email to a gmail user. Got back that it was not delivered.
Reporting-MTA: dns; mout-p-201.mailbox.org
X-Postfix-Queue-ID: 4hsN0y6XT9zMlN7
X-Postfix-Sender: rfc822; myemail@customDomain.com
Arrival-Date: Sat, 26 Sep 2026 11:43:14 +0200 (CEST)
Final-Recipient: rfc822; receiver@gmail.com
Original-Recipient: rfc822;receiver@gmail.com
Action: failed
Status: 5.7.26
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.26 Your email 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
[customDomain.com] with ip: [80.241.56.171] = did not pass 550-5.7.26 550-5.7.26
For instructions on setting up authentication, go to 550 5.7.26
https://support.google.com/mail/answer/81126#authentication
6a1803df08f44-91449f9bb91si10369466d6.229 - gsmtp
It worked before and I think I have set up everything correct.
EDIT: this is probably my own fault.
My problem is similar. I could not even send email to a gmail user. Got back that it was not delivered.
Reporting-MTA: dns; mout-p-201.mailbox.org
X-Postfix-Queue-ID: 4hsN0y6XT9zMlN7
X-Postfix-Sender: rfc822; myemail@customDomain.com
Arrival-Date: Sat, 26 Sep 2026 11:43:14 +0200 (CEST)
Final-Recipient: rfc822; receiver@gmail.com
Original-Recipient: rfc822;receiver@gmail.com
Action: failed
Status: 5.7.26
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.26 Your email 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
[customDomain.com] with ip: [80.241.56.171] = did not pass 550-5.7.26 550-5.7.26
For instructions on setting up authentication, go to 550 5.7.26
https://support.google.com/mail/answer/81126#authentication
6a1803df08f44-91449f9bb91si10369466d6.229 - gsmtp
It worked before and I think I have set up everything correct.
I'm afraid given the lack of response to the above queries I have had to move to Proton Mail. I have had no issues with delivery of emails, including to Gmail users. Hopefully Mailbox can sort this issue out as it is otherwise a really good platform.
I'm afraid given the lack of response to the above queries I have had to move to Proton Mail. I have had no issues with delivery of emails, including to Gmail users. Hopefully Mailbox can sort this issue out as it is otherwise a really good platform.
Agree, it would be nice if someone from mailbox would reply if this is fixable at all (although it's probably not mailbox fault, but gmail, but still, it's a problem if your mails are not received normally)
d.
Agree, it would be nice if someone from mailbox would reply if this is fixable at all (although it's probably not mailbox fault, but gmail, but still, it's a problem if your mails are not received normally)
d.
My suggestion is that you create a ticket in Mailbox support system and describe your problem. I got a quick reply when I did that so my problem is going away.
This is the documentation that helped me: https://kb.mailbox.org/en/private/custom-domains/spf-dkim-and-dmarc/
My suggestion is that you create a ticket in Mailbox support system and describe your problem. I got a quick reply when I did that so my problem is going away.
This is the documentation that helped me: https://kb.mailbox.org/en/private/custom-domains/spf-dkim-and-dmarc/
Dear users,
thank you for your reports, and please apologise the delayed response.
After a first analysis by our administrators, we can confirm that we have already implemented all possible measures on mailbox side (DKIM/SPF/DMARC). The headers of the affected emails do not reveal why Google is flagging the emails as spam. As the next step, we will submit an enquiry to Google regarding this case.
We will keep you updated and kindly ask you for some patience.
Kind regards
Your mailbox Team
---
Useful links:
Dear users,
thank you for your reports, and please apologise the delayed response.
After a first analysis by our administrators, we can confirm that we have already implemented all possible measures on mailbox side (DKIM/SPF/DMARC). The headers of the affected emails do not reveal why Google is flagging the emails as spam. As the next step, we will submit an enquiry to Google regarding this case.
We will keep you updated and kindly ask you for some patience.
Kind regards
Your mailbox Team
---
Useful links:
Replies have been locked on this page!