MAC is short for Migration Authorisation Code, and is a simple code requested by a broadband customer for switching their broadband provider. The MAC code system has been a voluntary scheme in the UK, which has been signed up to by the majority of large broadband providers, such as BT, AOL, Sky, TalkTalk, Orange and Plusnet.
On a new landline, or an existing landline without broadband, it can take up to two weeks to activate broadband upon that line. Likewise, if you cancel broadband on a landline, and the tag is removed, it would take a similar amount of time of activate a new provider upon that line. The role of a MAC code is to seamlessly switch providers with no loss of service.
Once you request a MAC code from an Internet Service Provider, it will typically take up to five days to arrive by post (usually 2-3 days). Once you hand over the MAC code to your new provider, it will typically take another five days for the service to change over. While you wait for your new provider to take over your service, your old provider will continue to supply broadband. Therein lies the purpose of a MAC code, to provide a relatively quick way of switching broadband providers with no loss of service.
The MAC code itself will typically be of 16 characters, and be a mix of letters and numbers. The MAC code is usually valid for 30 days, after that date you will have to request a new one. If you request a MAC code and do not use the MAC code, you need not do anything, your broadband service will remain with your current provider.