Occasionally someone will still mark it as spam because they are so used to marking all tzedakah emails as spam.
This could hurt the organization by the email providers automatically marking it as spam for other people.
It's good practice to have a (one click) Unsubscribe link easily found in your email for this exact reason, with people suggesting to even have it on top of the email.
As a general rule any emails I don't want to receive I try out the unsubscribe link, if that doesn't work I would then mark it as spam. What gets me more annoyed is the random texts that each get sent from a different number. I have recently started putting in my number as 1234567890.