Must you prove the defendant opened the email?

The short answer

No. Personal notice by data message does not require proof that the defendant opened the email. The Supreme Court explained this in its ruling of 3 June 2020 (case 11001-02-03-000-2020-01025-00): notice is complete when the email is received, and tying it to opening would leave its effect to the recipient's whim.

What is proved instead

Receipt. Paragraph 3 of article 8, as conditioned by C-420/2020, runs terms from when the sender receives an acknowledgement of receipt or access by the recipient can otherwise be established.

In STC16733-2022 the Supreme Court defined the acknowledgement as «confirmation that the message reached its destination», provable by any means: a voluntary acknowledgement, an automatic one, a postal company's record or the plaintiff's documents. Acceptance of the message by the recipient's server is an automated communication within the meaning of art. 20 of Ley 527 of 1999.

What opens are for

Supporting circumstantial evidence. An open or download record strengthens the proof, but has known technical limits: some mail services fetch images on their own, and others block them. There can be opens the recipient never made and reads that were never recorded.

That is why no part of Notificado's method makes notice depend on an open: it is recorded as circumstantial evidence and labelled as such in the record.

What does weaken the proof

A bare «sent» record when the defendant states under oath that the message never arrived. That is the line of STC690-2020 and paragraph 350 of C-420/2020. What makes the difference is proof that the destination server accepted the message.