The main reason is that on the occasion your hosting server goes down or experiences issues, both your website and emails will be affected. Other reasons include:
- emails will count towards your hosting space (a key consideration if you expect to send out or receive many attachments)
- you may have to lose your emails in the event you need to change your hosting
- emails from shared hosting environments may be blacklisted or flagged as spam (usually incorrectly) by large mail providers like Google’s Gmail, Microsoft and some government agencies due to their strict security protocols or a bad IP reputation.
- the email is basic and thus may lack some of the advanced features offered by commercial mail services
- emails on a shared hosting environment bring up the issue of privacy (a key consideration if you intend to send out highly sensitive messages)
Therefore, if you expect to use your email addresses as a primary means of communication or expect to receive or send very important emails, it’s advisable to consider using an email service that is specially geared for this task.