Hey, @Eduardo Kano and @genietim! How are you?
Some things can cause problems with Outlook. Some security blockers that may affect it but also, Outlook does not meet the same standards as other email servers like gmail, yahoo, thunderbird, etc. These emails accept formats that Outlook doesn’t, that is why it is ofter misconfigured. For Outlook, the recommended is always to use HTML and CSS 1.0 that is supported by them. This link shows you what outlook supports in terms of technical tags and HTML and CSS properties. 