There are times when people will decide that they need to stop receiving your communications. People wanting to leave the mailing list is disappointing but unfortunately an inevitable part of email marketing. Sometimes people move on from the company or simply change their mind. However, if you are seeing a large increase in the number of people who are opting out of your communications, you might want to consider reviewing your data and ask a few questions of it.

Are the emails and the content of them still relevant to the database of people I'm communicating with? 
The aim of email marketing, or indeed any form of marketing is to engage with people. In order to engage sucessfully with people you need to make sure that the content is relevant for them. This could mean reviewing your website and other points of contact/sign up for the customers and making sure that the information that you are sending out is inline with those points of entry.

Are my permissions correct and up to date?
Email marketing is opt in rather than opt out. What that means is that, the person who you are communicating with needs to give you permission to communicate with them in the first place, this is either by ticking a box to say "Send me details", give you their business card at an event, people that you have done business with, etc.

While the likes of the information commissioner say that if you are communicating B2B then you don't need their permission. The fact is that the Internet Service Providers (Hotmail, Google, Yahoo, etc) who actually deliver the emails don't quite see things as clear cut as that. They simply see an email being sent to an email address so the same rules apply with regards to opt ins, make sure you safeguard yourself.

Am I compliant with other spam guidelines including the Can-Spam Act.
The rules for email marketing can vary from country to country, we try and make sure that we have a best practice in place that covers most of them to ensure your safety online. These include making sure that you have a postal address, phone number, email address and an online method of unsubscribing on communications as well as our guidelines on opted in data.

Am I simply sending communications out too often? 
This could be the case, if you are sending something everyday, then the chances are that people will simply opt out or even just put you in their spam folder for all future emails. Why don't you ask your clients/customers/followers what they think by sending them a survey and finding out what they think about how you communicate with them. Engaging with them in different ways can be very enlightening!