Is white space allowed betwee mime header field-name and ':' separator

Question

Within a mime header, is white space allowed between the header field-name and \':\' separator? For example, are:

Content-Type: 

Answer 1

It isn't entirely clear whether it is or is not allowed, by the standard. However, implementations vary in how they handle whitespace between header field names and the colon. I would highly recommend avoiding whitespace there if you can.

The RFC for reference. This somewhat old article discusses the issue for HTTP headers, a similar standard.