This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Avatar for Username

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

This thread was archived. Please ask a new question if you need help.

5.1.7 Invalid sender address syntax when asking for notification

user1366614
user1366614
more options

when sending mail with notication to provider KPN I get an 5.1.7 Invalid sender address syntax when sending without notification of recieving no problems what to do?

when sending mail with notication to provider KPN I get an 5.1.7 Invalid sender address syntax when sending without notification of recieving no problems what to do?

Chosen solution

I heard about an undocumented solution: using mail.planet.nl, port 25, ssl, no username (!) all working again

Read this answer in context 👍 0

All Replies (2)

user1366614
user1366614 Question owner
more options

and I checked my sent mail header looking at the source of the message: there is no "Return-Receipt-To" ??? From - Mon Dec 12 06:22:20 2016 X-Mozilla-Status: 0001 X-Mozilla-Status2: 00800000 X-Mozilla-Keys: To: xxx@xxxxx.nl From: bbb <bbbbbb@planet.nl> Subject: test Message-ID: <f75a421a-b35f-4852-20de-316c3bf2f816@planet.nl> Date: Mon, 12 Dec 2016 06:22:19 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:45.0) Gecko/20100101 

Thunderbird/45.5.1

MIME-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit

user1366614
user1366614 Question owner
more options

Chosen Solution

I heard about an undocumented solution: using mail.planet.nl, port 25, ssl, no username (!) all working again