Gmail and other email service providers
The way Gmail and other email cloud services works entail that your mails will be received, stored and send from an external server, the same to which you also connect every time you request to see our use your inbox.
Amongst that information there are, without any doubt, personal data, which include for example, the email address from the sender and the recipient where these identify individuals and not legal entities, the message’s metadata and the content where that content gives information about an individual.
When the server is located in a third country or international organisation, like Google, in the US, for Gmail (gmail.com), or Microsoft, also in the US, for Outlook (outlook.com, live.com, hotmail.com and msn.com), you will be transferring personal data out of the EU.
Sometimes these big tech corporations are established in different countries and the controller entity which will process your personal data is not where their headquarters are located (the US in the previous example), but another company that they have established in European soil.
This is something to also take into account, because if the controller entity is based in European territory and it does not transfer the data overseas back to its headquarters then there might not be any international data transfers.