Can I adjust the limit for incoming attachments?

Technically speaking, Zammad knows only one global attachment limit. This is defined in the hosted setup with your product plan.
In the "Professional" plan, for example, e-mails up to 35 MB in size are allowed.

If you want to set the attachment limits for a specific person or generally lower than the global Zammad limit, you must configure this on your email server.

The differences between the versions, such as the attachment sizes ("limited attachments") can be found here.