I have a campaign with several emails that are sent in a sequence. Is there a way to include the content of the previous emails in each new email, similar to replying to an email in an email client?
My goal: If I refer to the content of a previous email, then the recipient should not have to search for their old email first, which they may have already deleted.
Is the content of the former mails dynamic or is it static content?
I have no idea as to how to do what you describe. But if the later (static content) you could create a landingpage with the content of every email and link to the content in your mails.
Currently, the content is static, except for the salutation. However, there may be A/B tests at some point, which will not make things any easier.
I think the idea of the landing page is not bad! I will definitely keep that in mind. Thanks for that! 
I have never used this plugin before but have seen it and it might be relevant for what you are trying to do: GitHub - karser/MauticColdEmailOutreachBundle: Send follow-ups in the same email thread for any A/B test variation
I have already tried the plugin. But it only seems to change the subject of the following emails to “Re: [subject of first email]”. Thanks for the tip anyway! 