There are two options in your profile to check:
"Always notify me of replies" and "Notify on new Private Message by Email."
Click on "My Account" at the top of each screen then select "Edit Profile" - the options are near the end of the page.
Making a post to a thread activates the alert system automatically so any further posts made to that thread will generate an alert.
You can also activate this manually by clicking on "Watch this topic for replies" at the foot of each page in a thread, so you'll receive update alerts even though you haven't posted to the thread.
Note: there is a bug in the WP forum software and this manual select/deselect will only work when you're viewing page 1 of a thread.
It's also worth checking that any spam-trapping service in use is configured to allow incoming mail from [email protected]
Spam-trapping is sometimes done by your mail provider or ISP, but may also be set up on your computer - eg. the Mozilla Thunderbird mail client has a built-in spam trapping system.
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Giraffe: a ruminant with a view.