- Add that person's e-mail address to your non-spam/junk filters.
- Add that person's e-mail address to your "It's OK, I like this person" list or whatever it might be called in your e-mail options.
- Check and double-check your own e-mail address as you supply it to them for a reply. If you can't correctly spell your own e-mail address you've got problems.
- Don't make the receiver go through one of the spam-blocking services by making them reply to an automated message first in order to be added to your list of acceptable addresses.
I've become pretty darned grumpy about that last one. When someone writes to me, I reply. When I get back the automated "please reply to message so that you can be added to my list of acceptable e-mail addresses" message I put my foot down. I don't reply. I delete. It really makes me grumpy because they wrote to me first.
Because e-mail is so easy to send it has also become easy to use to intrude on others without thinking first. Please be sure you use your e-mail wisely and think about the person at the receiving end. Especially if you hope to have a successful correspondence with them in the future.