Long ago it happened to me that only gmail took my emails as spam.
I contacted them commenting on my case and saying that it was an online store that I had and they solved it.
Then after a while I spent the same with hotmail, I contacted them and also solved it.
I don't think a dedicated ip is necessary, the hosting told me the same thing, but it was too expensive for me so I opted for new options.
Note: This is only valid if your email reaches almost all emails as normal.
If spam reaches all emails, your ip is banned in the blacklist of emails.
Edit. USE TLS port 587 in plugin SMTP
NO SSL
"The TLS (Transport Layer Security) protocol is the SSL successor protocol. TLS is an improved version of SSL. It works in a very similar way to SSL, using encryption that protects the transfer of data and information."