Make sure you can use their SMTP servers for outgoing email. Many hosting and domain name registration providers will not let you use their SMTP servers for sending emails. They assume you can send email via your internet server provider’s SMTP servers. However, a great many ISPs and broadband providers will only let you use their SMTP servers on their branded email accounts (i.e. [email protected]). This means that if you use your own email address (i.e. [email protected]), you won’t be able to send email via their SMTP servers. There are workarounds but you shouldn’t have to go to the trouble.
When looking up a bare name in DNS, the network stack will add the search domains to it to form fully qualified domain names, and look up those as well. For example, if the domain search list contains "wikipedia.org", typing "en" in the browser will direct the user to "en.wikipedia.org". Some ISPs add their own search domains via DHCP settings, similar to how they add DNS servers and other networking information; if this is undesired, the user can change this setting to ".local".
Be extremely cautious while communicating with the owner. Even if you casually agree to buy the domain via email, the communication might be used against you in court as a legally-binding contract should you change your mind. Until you’re absolutely certain that you want to make a deal, agree to buy the domain provided that all the terms are agreeable. This will leave you an escape hatch if things go south.
Contact the owner. Before so much as hinting at a price, simply email to ask whether or not the domain is for sale. If you are known or can clearly be linked to a thriving business, create a generic alternate email address through which to contact them, as your success might be leveraged against you. Be aware, however, that an informal-sounding email address is more likely to be regarded as spam or junk mail.
Even if the term isn’t trademarked, don’t buy domains that are just a variation of another domain name. This means avoiding plurals if the singular is taken (mediatemple.net vs. mediatemples.net), hyphenating a phrase (media-temple.net), or adding “my” or some other preposition (mymediatemple.net). Alternately, you might consider buying these variations yourself and set them up so that if someone types one of the variations, they are redirected to your main site.