Given the value of a mailing list, it’s astonishing how little care some people take with it.
Please, don’t send unsolicited emails- it is actually illegal to send emails to someone who hasn’t opted in to your list, unless they are a customer. It is OK to send emails to people who have purchased from you but pestering them with emails is not the way to win friends. It’s also good business practice because you get reported to ISPs (Internet Service Providers) as a spammer if you don’t. For the same reason, make it easy to unsubscribe.
Always send your emails from the web address you say it is. You may only be trying to be helpful because the address you are sending from is a bit obscure but, since this is what people trying to steal your bank details do, you are likely to be identified as a spammer. Spam filters will also pick up on certain words like ‘free’ and ‘discount’ because they sound like sales letters.
Once you are identified as a spammer (and apparently it takes very few bad reports), you may find yourself banned by your ISP or blocked by others. And that’s completely for all emails from your domain.