I currently have a php application called Sendy that connects via SMTP to Sendgrid and allow some of my customers send bulletins
(something like Mailchimp but simpler).

I charge extra for this service but have reached a point when my monthly bill is between $100 and $150 month so I am looking for
alternatives that can make be grow without spending more.

In my quest I found the following pieces of software that I am thinking of hosting by myself:
https://atech.blog/atech/postal-the-open-source-mail-platform
https://cuttlefish.io/

So I was wondering if you know some of them and can share some experiences.

I am just exploring and gaining knowledge. Have you considered using a platform like Postal?
 They are open source and available on Github. I am unable to include a link in this message, but you can try searching for it yourself.

My suggestion is that you use a three-step bulk email verification process (Syntax check, Verification of the email addresses domain, and Analysis of email server response) to clean your email list before sending out a campaign. This will help reduce any issues you may encounter during the sending process. Although Amazon SES is very cost-effective and efficient, there is always a risk of getting IPs blacklisted, which could happen due to your actions.

To prevent this, you should review the mail log to identify which IP addresses have been blacklisted, and then pause the campaign until the IPs are manually delisted. With SendGrid, you have the option to purchase a dedicated IP address and keep it clean, which provides better control over the situation. If you have the budget, I recommend investing in a dedicated IP or IPs, regardless of whether you choose to use Sendgrid or another company.

Sendinblue offers powerful and effective tools that enhance virtual business possibilities. With its efficient and presentable features, it serves as a marketing partner that not only assists with bulk emails but also helps promote products and services to boost growth.

Another tool is Hubspot, which serves as an email accumulation and sending solution for sending bulk emails, including marketing emails that can improve client relationships.

Pepipost is another reliable option for bulk mailing services. It API and SMTP services are used as a temporary email service that handles both sending and receiving bulk emails, as well as managing user actions like unsubscribing from email lists. It's more cost-effective than competitors, making it a popular choice for bulk emailing.

Amazon SES offers dedicated IP addresses, content filtering technologies, and a reputation dashboard that enhances sender reputation and ensures messages reach customers' inboxes. It eliminates significant upfront costs and contract negotiations, providing a mature email infrastructure and experience gained over the years.

Postal is an open-source mail platform that allows you to send and receive emails. It provides features like email tracking, analytics, and automation. Cuttlefish, on the other hand, is a self-hosted email marketing platform that focuses on simplicity and ease of use.

Both Postal and Cuttlefish can be alternatives to Sendy and will allow you to host your own email service. However, it's important to note that self-hosting requires technical knowledge and maintenance to ensure proper functioning and security.

Before making a decision, it's a good idea to research more about the features, support, and community behind each software. You can also consider factors like scalability, ease of integration with your existing system, and long-term costs. Additionally, it may be helpful to look for user reviews or seek advice from other users who have experience with these software options.

Use a three-step bulk email verification process: syntax check, domain verification, and email server analysis, to clean your list before sending campaigns. Monitor and delist blacklisted IPs to prevent issues. Consider a dedicated IP with SendGrid for better control and improved email reputation.