Swiss service claims to use heavy encryption and local privacy laws to protect users.
Encrypted mail service ProtonMail has closed its beta signups after 60 hours following a server crash due to overwhelming demand.
Founded by three CERN scientists in Geneva, Switzerland, last summer, the service opened its beta last week promising to safeguard the privacy of its users through extensive encryption and stringent Swiss data laws.
"When we launched ProtonMail, we did not anticipate that there would be so much interest in our service," the firm said. "We thought we had enough resources in place to support over one month of user signups."
The service aims to provide the strongest encryption possible while still being accessible through a web browser, with developers describing it as akin to a more secure Gmail.
Swiss data protection agency FDPIC refuses to transfer data abroad if it feels the recipient cannot provide "an adequate level of data protection", and firms acquiring or processing people's data are required to give reasons.
ProtonMail has warned that their service is still vulnerable when computers accessing emails are compromised, but claims to have guarded against man-in-the-middle (MitM) attacks, where a criminal will eavesdrop on a conversation, and backdoor attacks which would target the main servers.
Tomás Touceda, a privacy officer at cloud firm SpiderOak, said: "Currently, with the technology we have, there is no way for a system to truly verify that the friend you are exchanging mails with, chatting, or sharing files securely is who he says he is.
"More so, there is no way to verify that nobody is 'in the middle' of your exchange of data. In the security world, having this kind of vulnerability is as good as having no security at all."
Source: Company Press Release