They are not interchangeable, and approaching the wrong one wastes the approach. The difference is simple: one owns the role, the other owns the process.
They will manage whoever is hired. They wrote or shaped the job description, they decide what “good” looks like, and they make the final call. They are usually not in the applicant tracking system all day, which means a direct note stands out rather than joining a queue. They can also do something no recruiter can: decide you are interesting enough to talk to regardless of what the filters said.
Internal recruiters run the pipeline — screening, scheduling, offers, and often the first filter. They see every applicant, which means they are both the most informed person about where you stand and the busiest. They can move you forward, unstick a stalled application and tell you what is actually being weighted. What they usually cannot do is overrule the hiring manager's judgement about fit.
An external or agency recruiter works for the employer, not for you, and is paid on placement. That is not a reason to avoid them, but it does change the advice: they are a route to roles, not an advocate for your candidacy, and they cannot tell the hiring manager to reconsider you.
The name, the title and a verified address, for every job you apply to.
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