Public cloud servers are great for many things; however, sending email is not one of them.
Why Cloud Servers are Bad for Sending Email?
The main issue with public cloud based services is that you are sharing resources with their other customers. This includes IP addresses. Most organizations try to filter out bad IPs, but when joining a new service there is a chance you could be assigned an IP with a poor reputation.
The IP address spaces used by the major public cloud vendors (i.e. Amazon, Rackspace, etc.) for their cloud servers are well known and are generally black- or gray-listed by anti-spam systems. This can slow or altogether stop emails sent from those IPs to getting to inboxes. Additionally, many of the IP addresses in use by these systems are flagged from previous abusive use by spammers. When setting up a new cloud server, you could be easily assigned one of these flagged IP addresses. Even if you do not inherit a bad IP reputation from the previous user(s), your server will be listed as a public cloud IP address. As a result, it may suffer from the “bad neighborhood effect” and thus considered a possible spam source.
We have investigated several services that claim to offer “Cloud-Based Outbound Email” and have found that many use cloud servers for things like scanning email messages for spam and viruses, but use non-public cloud servers for the actual sending of email. This is obviously not true for all companies, but if everyone might be affected, the solution is to NOT send email directly from your public cloud. There are, however, straight-forward solutions to getting email originating from such servers delivered.
How Did Cloud Servers get a Bad Email Reputation?
The “utility computing” model of the cloud is to blame. In the interest of making these services as cheap as possible, there are generally very few services included. In particular, you get 1) minimal customer support, 2) little pre-sales work, and 3) minimal, if any, validation of new customers. All that time would increase prices. As a result, it is easy for a spammer to signup with a name and credit card. To start sending spam, all they need to do is agree to “terms and conditions” by checking a box. (How much do spammers care about that?)
Spammers and fraudsters take advantage of this simple workflow to setup servers for sending spam or performing other abusive actions. They do not care if they get shutdown fairly quickly because:
- They are using stolen credentials and payment information,
- It is so easy to setup a basic cloud server, that there is not much time lost, and
- Even if they get shut down “fairly quickly,” they have still sent some of their spam, etc.
Once they get shut down, spammers choose another public cloud provider and use another stolen identity to do it again. They can even automate this signup process by using the available APIs for these services.
The above scenario contributes to the pollution of the reputation of IP addresses and the public cloud servers in general.
Why Private Cloud Servers Are Better for Sending Email
With physical dedicated and managed servers and private clouds, you typically interact with a sales representative, sign a contract, and undergo some level of validation (even if that happens behind the scenes). The time it takes to sign up blocks most spammers who use these services and keeps these IP address spaces much cleaner. The more validation and attention that is offered by a sales staff before signing up their customers, the cleaner the IPs are.
If you are sending large quantities of important email from a cloud server, consider using LuxSci Secure High Volume Email Sending to avoid the risk of your emails getting blocked by spam filtering services. Using a trusted private provider will mitigate the bad neighborhood effect and significantly increase the deliverability of your email. Unlike in a public cloud, you can add additional dedicated resources to ramp up throughput for business critical emails.
In many ways, the Internet is still like the Wild Wild West. Email messages sent to you or from you can and do “go missing” for no apparent reason. This can happen no matter what email provider you use. So, what happened to these “AWOL” messages? How can you diagnose and solve the problem? 
It happens over and over — users trying to send legitimate email messages are blocked from sending because the IP address that they are getting from their Internet Service Provider (ISP) for their personal computer (or small office) is on some major blacklist, like 
