Mail Rentaway Server presents an interface that is at first glance, complex and perhaps intimidating for users who are not comfortable with a high degree of technical language. The navigation element outlined on the platform mentions elements like Webmail, ConsultantPlus, and detailed client email settings. These can be a daunting prospect for the novice user, but for the more tech-savvy users, may be seen as a promising indication of the functionality available on the site.

The mail server offers settings for the Pop/POP3 or IMAP server selection. This is a typical feature in mail server systems, allowing users to determine the internet message access protocol that suits their usage requirements. However, the lack of clear guidance on which option would be most suitable for different types of users may leave some users feeling uncertain about their selection.

The user instructions request the input of the 'full address of the email client'. This is, of course, a standard requirement. However, users who are unfamiliar with such terms might have to resort to external help or internet resources to understand what is needed, thus potentially interrupting their workflow. Expert users, on the other hand, might appreciate this straightforward and no-nonsense approach.

A significant advantage that the Mail Rentaway Server offers is the secured password check (SPA). In ensuring high data security standards, users can have peace of mind when it comes to the protection of their private information and communications. To further enhance its security measures, it offers secured connections (SSL/TLS) through ports: imap - 993, pop3 - 995, and smtp - 465. This is a valued feature, particularly in an era where data security is a priority.

Perhaps the most arresting feature is the STARTTLS connection, an extension commonly used to offer a way to upgrade a plain text connection to an encrypted (TLS or SSL) connection instead, hence proving that the Mail Rentaway Server is a platform that values secured exchanges. Ports utilized for this are imap - 143, pop3 - 110, smtp - 25.

Yet, one potential downside for some users might be that this platform offers no apparent customer support or help center information on the homepage, a shortfall that contrasts with the complex nature of the tasks users are left to navigate independently.

In conclusion, the Mail Rentaway Server is a robust mail server system that appeals primarily to technically confident users. It boasts an array of necessary features, promising functionality and robust security. However, its somewhat technical approach and lack of visible customer support could potentially alienate less tech-savvy users. Despite this minor drawback, Mail Rentaway Server has many features that make it stand strong in the face of many competing mail servers. The system's focus on safety, security, and adherence to standard conventions show promise for a strongly competitive, reliable mail server.