Obviously, don't donate blood if it causes you to pass out. But that's a pretty rare side effect, and mostly people can donate without any negative impact.
You should not pass out, and the mail/email can be easily unsubscribed from.
Almost no junk mail can be easily unsubscribed from in my experience.
I unsubscribed for almost all junk mail without any problem (save for spam, but that's different matter)...
How? Do you just write back and ask them to stop?
Many literally have a link at the bottom that says "unsubscribe". I've received emails from dozens of different services and companies over the past few years and every single one, without exception, has had this feature. It's prevalent enough that my email client even attempts to find it and presents me with a button in the UI if it does.
Notably CAN-SPAM act requires spam to have effective and visible unsubscribe links. While this doesn't impact off-brand Viagra and Nigerian prince spammers, most legitimate US businesses (such as American Red Cross) should be compliant.
Why the minuses?
I don't share my email all over the web, I usually don't sign up to many websites. If I do in majority of cases (99% I would say) there is included option to manage my subscriptions and/or unsubscribe directly from the message... and it works.
Every email that I have received from a legitimate organization in the past several years has had a one- or two-click unsubscribe link at the bottom. I can't get access to the Red Cross' reminder emails right now, but given what the Red Cross is, it's rather likely that the parent is telling the truth.
Edit: parent
Sorry, I meant physical mail not email.
My pressure sometimes would drop just after the donation while still in the seat, until I figured out it was due to dehydration; the one thing that solves the issue completely for me is drinking plenty of water the day before.
It's a little difficult. If you have type O blood the American Red Cross will bug you incessantly when you're able to donate again. While it's nice to be in demand, it's still annoying. You can ask them to knock it off but there's no option for once a month reminders.
I hate to say it but you are right about this. I donate frequently and encourage everyone who can to do it but the Red Cross spam operation is absolutely disgraceful they have zero shame.
If it works, isn't it more ethical to annoy people in this case?
It's annoying but I don't mind it like I do the daily business loan cold calls.
I'm just glad you were able to corellate saving lives and spam emails. /s