Plugin (or workaround) to see images inline in emails

Hello all,
I have inherited a redmine installation 4.1.0.stable. There are no plugins.

Emails sent via SMTP (I've setup a gmail account for this) don't display images. From a bit of research I either need to allow anonymous access (not a good idea for us) or use a plugin. Is anyone on this version using a plugin for this? Or another way I've missed?

Many thanks