You need to weigh up the pros and cons for what you're optimising for e.g. cost, robustness, security, setup time. Separating them is likely more secure and rob

You need to weigh up the pros and cons for what you're optimising for e.g. cost, robustness, security, setup time. Separating them is likely more secure and robust, but likely more costly and requires more setup. Why not use a mail service instead of hosting yourself?