two-factor authentication (2FA) and SMS received from sender other than Dropbox

[DM79]

To access my Dropbox, I use double authentication, two-factor authentication (2FA): I receive a text message on my mobile phone with a temporary code to enter. Normally the sender of the sms is named Dropbox, but today I receive the momentary code from an unknown number (like+39 351... or +44 7468....). Can I consider it safe? Or must the Sender of the SMS message be only and exclusively DROPBOX?

[Nancy]

Hi @DM79, and thanks for posting this here. 

Just to clarify, does this code arrive at your mobile number as soon as you generate it? 

How many times did you try to generate the code and you saw this? 

Let me know, and we’ll have a closer look.