14 DAY TRIAL // You can have a lot of problems if you don't know how to send an e-mail. And I'm serious - though legitimate, it may be blocked by spam filters. And you do want your mails to arrive where their are supposed to, don't you?
Well, spam filters are sometimes very strict and they block non-spam messages on different criteria. For example - some time ago, I was sending e-mails to a colleague that was two feet away from me and after sending him more than 5 mails in a rather short interval, his mail client flagged me as a spammer. That happened because he didn't have me registered in his contact list. However, not all the people one sends e-mails to have the sender in their contact lists. This could be an issue, should one wish to send a lot of e-mails.
In addition, there can be other problems as well, when regarding over-zealous spam filters, as I've learned from MailChimp's website. There are certain words or behaviors that spam filters recognize as spam. For example, using caps lock or lots of exclamation marks could get your message sent to the bulk folder. Also, the usage of spam-like phrases will get you "filtered" - include things like "Click here now!" or "This is great! Cilck!!!" and your message just might get lost in cyber-space, heading for a bulk folder, never reaching the inbox you whished it to reach to.
I've just experimented this with a colleague's Yahoo! e-mail address. I sent him a message with "VIAGRA CIALIS REALLY CHEAP!!!" in the title. He got the message in his inbox, but had he clicked the "this is spam" button, the next time I would have sent him a message with the same title, it would have gone straight to the bulk folder. This is the way spam-filters try to adapt to new situations. So, the basic idea is: when you send an e-mail, no matter if it's legitimate, make sure it doesn't look like spam, or it will never get there.