use httpS;// in your URL (UPN) http://links.notification.intuit.com/ls/click?upn=1Wi9rq4VfPfKgsLy2CqOasM7fwlvmmTDHVRYQ3453hxRAIwTTPW ...
use httpS:// in your emailed Invoice link.
Additionally, because the URL (UPN get parameter) is LONG and
has unfriendly characters in it, older installed Outlook mailreaders will not click-to-open nor "Copy Hyperlink"
There's no need for such a convoluted UPN parameter.

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Anonymous commented
To rub salt in the wound, there is no mention that for "posting a suggetion" one needs to HAVE AN ACCOUNT.
The same problem occurs when trying to respond to the email verification email - one cannot click on the link from an older Outlook mailreader installed app.
FURTHER, in the confirmation email, the DARK BLUE TEXT ON DARK VIOLET BACKGROUND IS UNREADABLE.
CONCLUSION - INTUIT JUST DOES NOT WANT FEEDBACK