List-unsubscribe link is not always appearing in ISP's

[SorenDP]

HI Community! 

We have been working on a list-unsubscribe hybrid solution supporting both one-click as well as mailto: options.  

While testing this however, I am experiencing that the unsubscribe link is not consistently appearing in the emails, but only sometimes. 
I am really puzzled about why this is and also a bit concerned with implementing the headers, since I am not 100% confident with my test results since it does not always work. 
This behaviour is observed in both apple mail app, as well as gmail app + web. 

I can confirm that both the mailto: as well as the http post request are indeed working, just not always showing. 

Any clue why this may be the case? 

Thanks a bunch! 

[_Pascal1976_1]

Hello,
can you share the email headers of a message received on Gmail please ?

[SorenDP]

Hi @_Pascal1976_1!  

Sure thing:

List-Unsubscribe: <https://domain.com/oneClickOptOut.jssp?id=@7JBrzEYGpnDQTlgR/wJarr39JJASszYx96q1rsins6v219OK4XNHGCRnu3A8svZT>, < mailto:tv2@domain.com?subject=unsubscribeMESSAGEID>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

[Tobias_Lohmann]

Hi SorenDP,

as per my experience we can only "offer" the correct headers to the ESPs, but whether or not they'll display the button in their UI or is completely up to them. I think I observed, that the button usually appears in times when there is a higher sending volume, but I can be wrong on that.

On the official Gmail help pages it is mentioned though, that they will enforce the necessity of those headers only for email senders with a marketing email volume above 5000 emails per day. So if the volume is lower during your tests it could be that Gmail simply doesn't consider it as relevant and won't show the button. That's my best guess  

Best regards, Tobias