Sender ID Usually a dedicated virtual mobile number (VMN) or short code found in the NUMBERS section of your account. If no value is set here, it will default to the shared Sender ID for the country you are sending to. Can also be an 11 character alphanumeric sender if available for the destination country. You will need to click on the Add Sender ID button found in the NUMBERS section of your account in order to request the use of an Alphanumeric Sender ID. Sender ID functionality varies by country. Global Sender ID Information Mobile and dedicated VMN's should be in international format. Alphanumeric senders (cannot be replied to) can have a maximum of 11 characters. No spaces. If opt out is required, using Custom Sender ID, use parameter [unsub-reply-link] in message to insert opt out link.