MailAddress constructor inconsistency

[naasking]

MailAddress is inconsistent in how it handles special characters in the display name portion of an address. Try the following code on any version of .NET, including .NET5:

using System;
using System.Net.Mail;

namespace MailAddressTest
{
    class Program
    {
        static void Main(string[] args)
        {
            // display name accepts a name with \
            var ok = new MailAddress("foo@foo.com", "Foo \\ Bar");

            try
            {
                // however, the generated address fails to round-trip
                var fail1 = new MailAddress(ok.ToString());
            }
            catch (FormatException e)
            {
                Console.WriteLine($"Fail1: {e.Message}");
            }
            try
            {
                // parsing an address from a string also fails for the same reason
                var fail2 = new MailAddress("\"Foo \\ Bar\" <foo@foo.com>");
            }
            catch (FormatException e)
            {
                Console.WriteLine($"Fail2: {e.Message}");
            }
        }
    }
}

I think the expectation is that round-tripping the mail address should always work, so the MaillAddress constructor that accepts separate display name and address parameters should perform the same parsing checks on the display name as the single-parameter constructor.

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Issue Details

---

MailAddress is inconsistent in how it handles special characters in the display name portion of an address. Try the following code on any version of .NET, including .NET5:

using System;
using System.Net.Mail;

namespace MailAddressTest
{
    class Program
    {
        static void Main(string[] args)
        {
            // display name accepts a name with \
            var ok = new MailAddress("foo@foo.com", "Foo \\ Bar");

            try
            {
                // however, the generated address fails to round-trip
                var fail1 = new MailAddress(ok.ToString());
            }
            catch (FormatException e)
            {
                Console.WriteLine($"Fail1: {e.Message}");
            }
            try
            {
                // parsing an address from a string also fails for the same reason
                var fail2 = new MailAddress("\"Foo \\ Bar\" <foo@foo.com>");
            }
            catch (FormatException e)
            {
                Console.WriteLine($"Fail2: {e.Message}");
            }
        }
    }
}

I think the expectation is that round-tripping the mail address should always work, so the MaillAddress constructor that accepts separate display name and address parameters should perform the same parsing checks on the display name as the single-parameter constructor.

Author:	naasking
Assignees:	-
Labels:	area-System.Net, untriaged
Milestone:	-

[danmoseley]

Question is how breaking would it be to existing code to change this.

[danmoseley]

Noting this isn't a regression so I assume it won't meet the 6.0 bar.

[naasking]

Question is how breaking would it be to existing code to change this.

Unclear. The currently accepted input appears to reject a lot of valid email addresses. Of course, some code in the wild might depend on MailAddress rejecting that set of email addresses. Not sure what the policy is on this.

[ManickaP]

Triage: needs investigation in mail address format standards. If '\' is allowed character in display name we might consider fixing this.
AFAIK, if you don't use special characters in display name, the round trip works. But this needs to be confirmed as well.
This is future work, it's been like this for a while.

[naasking]

Triage: needs investigation in mail address format standards. If '' is allowed character in display name we might consider fixing this.

Just to be clear, I think there's a bug here even if '\' is not allowed. The 2-parameter constructor should throw an error in that case but it doesn't.