A dedicated IP address is intended only for one user, company, client. It means:
Maximum risk reduction – thanks to a dedicated IP or a subnet of IP addresses, you do not share the process of sending your e-mails with other companies. Third-party e-mail senders will have no impact on your reputation and the deliverability of your mailings.
No queuing – you decide how many messages you send at any given time. The lack of other companies in the queue means that you are not dependent on them if they plan campaigns to be sent earlier. However, it is worth sending the e-mailing campaign in batches (e.g. 5000 each), if it is a larger address database, so as not to immobilise the server and the e-mailing service.
Personalised DKIM – a key that protects against phishing and positively affects the deliverability of your e-mails. When you direct DKIM to your own domain, a good sender's reputation will be assigned to your IP address as well as your domain. Thanks to this, after changing the server/service provider, you will be able to enjoy high deliverability almost immediately.
It is worth having several IP addresses or a whole subnet so that in case one of the IP addresses is blocked for some unexpected reason, you will be able to use another one.
A shared IP address therefore means:
Common reputation of all senders – if you know you share your IP address with trusted users who follow good mailing practices, you can be relatively confident about your mailings. However, it only takes one black sheep for suppliers to reduce their reputation and deliverability to an entire user group. Additionally, even one or two mailings can make all e-mails from a shared IP address start falling into SPAM. Do you know who you share your IP address with?
Co-presence on blacklists – blacklists are a collection of blocked IP addresses and/or domains. If a shared address is included in this list for some reason, your messages will not be delivered to the recipients. The removal process from the blacklist is very cumbersome and time-consuming.
Message queuing – if any of the companies decides to send up to several hundred thousand or million e-mails, the risk that your messages will end up in the queue and be delivered with a delay increases greatly. It may happen that Internet operators limit the number of e-mail messages received from a given IP address or IP addresses during a given period of time (e.g. hours). Thus, such a process is very burdensome in the case of sending a large number of transactional messages that need to be delivered, e.g. within a few seconds.
Incorrect sorting of messages – large mailings of marketing messages from one or a subnet of IP addresses may cause Internet operator filters to classify all messages from this source to the same tab in the user's email application, e.g. Offers or SPAM, and this will cause the user to may not find out about the company sending such a message.