Easy way to know whether a job offer is real or scam

I am a health professional in Canada.

Years back, I posted my CV to work in the middle east on a job site in the gulf. Last week, I got 3 emails claiming from a general hospital in Abu Dhabi, a hospital Dubai and another medicare hospital in Dubai for online recruitment.

they showed interest in my CV. All emails were from free accounts (gmail.com address). I chose then to forward an email to the concerned HR department of the concerned hospitals.

I forwarded one email to the official email of one of the hospitals (as given on the hospital site). They replied and said, yes, the email is legitimate and you can apply with confidence.

Now I got an offer letter from Dubai hospital with handsome salary offer but from a Gmail address. They're asking me to start position in one month only and asking to contact a travel agency based in Dubai.

Is it a scam or true? I have forwarded the email to the HR department of the hospital to determine authenticity.