Fixed or Dynamic IP address?
What’s an IP address?
Let's start with the basics. An IP address is a unique number that you are assigned when you connect to the internet. It's a little like getting a number when you join the army. An IP address is a way of identifying you as you use the internet. It is formatted as strings of numbers separated by dots. There are up to three numbers before each dot that range between 1 and 255. Here's an example - 188.8.131.52 is the IP address of Google's DNS service.
Limited availability (sold out soon!)
There are only so many IP addresses going around (3,706,452,992 to be precise). Sounds like an awful lot, doesn't it? It certainly did in the early days of the web, but less so now. In fact, the number of available IP addresses is running out. Predictions vary, but we've only got a limited time available using the current format of IP address. It is the scarcity of IP addresses that has meant that the people who assign them when you connect to the internet (typically your Internet Service Provider) often try to stretch what they have. They have a pool of addresses that they share out between their customers. This is based on the premise that not every single one of an ISP's customers will connect to the internet at exactly the same time so there will be enough to go around. This system of sharing IP addresses is called a dynamic IP address system.
What’s wrong with being dynamic?
There can be drawbacks in being a part of a dynamic IP address system, one of the main ones being problems sending email messages. Here's why. Not everyone who is an ISP's customer is as well behaved or computer savvy as you. When you connect to the internet you may inherit an IP address that was previously used by someone who was misbehaving (or, more likely, their computer was misbehaving). The previous user of an IP address may have connected to the internet and sent out a lot of junk email. The most likely probability of this is that the previous user has/had some nasty software (malware, virus, call it what you will) on their computer set up with the sole intention of sending out thousands or millions of spam email messages.
The offending IP address is soon picked up by what are called RBL systems (Remote Black Lists). RBLs are, in essence, big databases full of IP addresses of computers that are sending out junk email messages. Almost every good email server will refer to one of these RBL services (there are quite a few - take a look) before deciding whether to accept and process an email message. An IP address may be stored by an RBL for a short period of time if the activity from that address is short lived or on a more permanent basis.
Why email messages go astray
If your IP address has found its way onto an RBL list the end result is that your email messages don't always go where they are supposed to. Your IP address may only be stored in one or two RBL databases and so the majority of your messages will go to your intended recipients without a problem, but some recipient's email servers may check precisely the RBL database that your IP address is listed in and block your messages. This can lead to a lot of frustration - "I don't get it. Most of my messages go through fine, but some never make it".
What can you do about it?
If you are having the sorts of problems described above there are two potential solutions:
Get a fixed IP address
If you always wanted the same IP address every time you connect to the internet you will need to request a fixed IP address from your ISP. This often comes at an additional monthly charge. It does mean that you are the only person using this address so you can't blame anyone else if it gets black listed.
Disconnect and reconnect to your ISP
You should, in theory, be assigned a new IP address from your ISP's pool. Fingers crossed that this too isn't RBL black listed ...
Some Helpful Tools to use
What's your IP address?
Check for a blocked IP address