Petland rejects my email

So, like a number of other people who received the email from the Humane Society of the United States (HSUS) regarding their investigation of Petland pet stores and their connection to puppy mills, I signed the action form that sends an email to Petland asking them to stop selling puppy mill puppies.

Twenty-four hours later I got the always popular delivery failure notice.

The following message to <operations@petland.com> was undeliverable.
The reason for the problem:
5.4.7 - Delivery expired (message too old) 421-'4.4.5 Directory harvest attack detected'

Petland Headquarters
250 Riverside Street
Chillicothe, OH 45601

Dear Petland Headquarters,

Despite assurances by staff at many Petland stores visited by
The HSUS and on Petland's corporate website that the company
knows its breeders and deals only with those who have "the
highest standards of pet care," many of the puppies sold at
Petland stores come from massive commercial breeders in Missouri
and other Midwestern puppy mill states, where hundreds of
breeding dogs are packed into cramped, barren cages. This
support of cruelty needs to end now!

I will not only not spend a dime in your stores, I will continue
to tell as many people as I can, both face-to-face and via the
Internet, to stop supporting you until you end your practice of
carrying puppies.

Honestly, I have no idea how you all sleep at night.

Regards,

xxxxxxxx

I guess a harvest attack is some tech term describing a bombardment of emails, which sort of makes sense given that the HSUS has a pretty good reach. There certainly wasn't anything attached to the email, nor did I send multiple versions. No matter, I'll just try again outside the HSUS system.