Outlook Blocking email from Thunderbird
I have been having issues with my email not being received by users on Microsoft's Web Mail serivces (live,outlook,hotmail..). My email address is on my own domain and I've checked the SPF and DKIM records which are perfectly fine. The emails are sent without problems to other domains. Its only Outlook that has a problem receiving from Thunderbird. While sending the same email with the same TO and FROM address via the webmail interface, Outlook has no problem receiving.
I've checked the Troubleshooting guide on [https://sendersupport.olc.protection..../troubleshooting.aspx] and its of not much help.
I even tried comparing the recieved emails' source with the one that gets delivered WebMail->Outlook+GMAIL and the same email sent from Thunderbird->Outlook+GMAIL.
The only noticeable difference in the source is that the HELO=value is different. Thunderbird sends my Computer's local IP address as the value.
I've tried changing that too hoping to see it work, since the Outlook Troubleshooting guide mentions :-
"We may not accept email from senders who fail a reverse-DNS lookup. In some cases legitimate senders advertise themselves incorrectly as a non-internet routable IP when attempting to open a connection to Outlook.com"
But this too did not work. Usually If an email is blocked by Outlook and I enable DSN, It would alert me to the reason. In this case I don't receive any notifications.
Since its just specific case of Thunderbird->Outlook address that is not delivered due to filtering by Microsoft. Can anyone point me in the right direction? Why are only emails sent from Thunderbird being blocked ?
الحل المُختار
I would do a series of tests to see if the blocking is due to a specific type of content. First, send a message with plain text and nothing else, then a message with a signature with a local image, then a message with an image stored on a remote server, then a message with a link etc. Does this happen just with TB or other desktop (not webmail) apps?
Read this answer in context 👍 1All Replies (6)
الحل المُختار
I would do a series of tests to see if the blocking is due to a specific type of content. First, send a message with plain text and nothing else, then a message with a signature with a local image, then a message with an image stored on a remote server, then a message with a link etc. Does this happen just with TB or other desktop (not webmail) apps?
Thanks for your reply, Until now, I've been testing with only plain text. I tried sending different content but still isn't being received.
Strangely, while testing with other email apps the same thing happens. I've tried it with eM Client & Mailbird. With the exception of Spike, which seems to be functioning like a webapp and sending the email from their servers.
I never expected email would be dependent on the computer's configuration. Meanwhile, I'll try it on someother computer..
I've tried various things. It just doesn't work when sent from any standard Mail App. And Its not limited to Thunderbird.
It works fine when using Apps, like Spike/Outlook Mobile App, that send the mail from their IPs/Servers.
I guess, it has something to do with their "Junk Email Reporting Program" which blocks initially unknown IPs from sending email. It looks like I have to get my telecom provider to enable the IPs for sending email which seems like a chore given that we are assigned dynamic IPs.
Modified by Maruthi S
This might help...
read comments by rsx11m regarding eg: 'mail.smtpserver.smtp1.hello_argument'
read workaround:
Thanks for the links. But like I mentioned earlier I did try changing the Helo values and it had no effect.
But I did try with another hosting provider, and found that emails are delivered when using STARTTLS mode but not SSL/TLS. On the receiving side, I noticed the difference in header showing TLS v1 as against TLS v1.2 and the TLS v1 had no Helo argument on message. By that I don't mean Helo was null or anything. It just wasn't there.
And I don't understand any of this. Thanks for the help though. Clearly its not an issue with Thunderbird. I'll just leave this open for a couple of days and close the thread.
P.S. Email has become so complicated since I last handled such things 15 years back, just want to give up and go back to webmail. I never expected to be troubleshooting SMTP.
Just a point to add. The same emails that are being blocked, go through if they are reply to an email. In such instances the headers automatically include some reference to Microsoft Protection...something...