#11楼 @rei 嗯，如果网站和 Email 功能结合紧密的，又要考虑到成本和经验积累，自建的确是个好选择。
不过，我不太赞同独立 IP 可以解决 IP limit，我贴一段 Mailgun 的详细说明，从多种情况进行了分析：
Do I need a dedicated IP address?
It depends on various factors.
If you are sending a lot of email (greater than 50k per week), it is a good idea to have a dedicated IP in order to isolate your reputation. If you are sharing your IP, you are sharing your reputation with those other senders. In addition, ESPs limit the total volume per IP, per hour. If you are a high volume sender you should consider a pool of IPs. However, you will have trouble establishing your reputation if you are not sending enough volume consistently from an IP - in this case, a shared IP is preferred.
If your email sending is volatile with large spikes of volume, ESPs may assume those large spikes are spam. Also, if your overall volume is too low, they won’t acknowledge your reputation. Generally, if you are sending less than 5,000 emails per day, a shared IP may be the right solution.
The other thing to consider is using separate IPs for your bulk and transactional mail. There are a couple reasons for this:
Delivery of time-sensitive transactional emails may get queued behind a large batch of bulk/marketing emails.
Your transactional mail will be affected by the reputation created by your bulk/marketing mail.
Mailgun’s infrastructure mitigates some of the argument’s for a dedicated IP address. First of all, we are constantly monitoring our shared IP addresses for any reputation issues. We also allow you to schedule delivery of your emails by using the o:deliverytime parameter. This allows you to delay the delivery by using a time in the future and also allows you to jump other messages in your queue (say from a large bulk mailing) by using a delivery time of now.