Send the authenticated emails that will be no problem. In a small service I manage, more than 80,000 emails have been sent every day for more than 10 years and have never been spammed. Eventually you may have problems regarding reverse dns, email headers and dns definitions. But they are relatively simple things to solve. And also, avoid sending to those who do not authorize the receipt, because when doing so the person who receives normally denounces and thus will foul the domain until it falls into the public databases of spammers. At this point you will have some difficulty in requesting removal.
One should also be careful that it is not enough just to send authenticated. You also need to make sure the limits and standards of the environment, the server where the script will run. Usually shared hosting detects long runs and blocks them. Others allow continuous executions, but detect sending emails and impose a limit of 100 to 400 emails daily or monthly. Anyway, you should consult the rules of your hosting provider.
Another note is the mail server that will be used to authenticate the submissions. One should also note the limits of this mail server. For example, gmail has a limit of 400 emails per day, but this limit varies with the type of account used.
1. Verifique as normas e limites do servidor de hospedagem
2. Verifique as normas e limites do servidor do email usado para autenticar
3. Verifique configurações de DNS reverso tanto para IPV4 quanto para IPV6
4. Não camufle o domínio do email que está enviando. seja o mais transparente possível
The negative point of authenticated submission is the delay in submissions. Because each submission requires authentication. You can send legitimate emails without falling into spamlists, using the native mail () function, without authentication. But for this the server must be well configured. The important thing is that the sending server can be recognized and "audited" remotely in relation to its identity. In this case, the checks are made by the DNS settings. Therefore, avoid sending from a server that does not have a DNS domain. A subdomain can be used, for example.
However, the volume you want to send is small. It is possible to execute everything in less than 1 second even authenticated. This will require asynchronous execution techniques.