503 Sender already specified

[peffis]

Sometimes, when there is a lot of sending going on I get a "503 Sender already specified" from pool.Send() when the pool has been instantiated with

pool, err := smtppool.New(smtppool.Opt{
                Host:            os.Getenv("SMTP_HOST"),
                Port:            587,
                MaxConns:        10,
                IdleTimeout:     time.Second * 10,
                PoolWaitTimeout: time.Second * 3,
                Auth: smtp.PlainAuth("",
                        os.Getenv("SMTP_USERNAME"),
                        os.Getenv("SMTP_PASSWORD"),
                        os.Getenv("SMTP_HOST")),
                TLSConfig: &tls.Config{ServerName: os.Getenv("SMTP_HOST")},
        })

There seems to be some race condition going on possibly where a connection gets used by a different send request and I wonder if this explains also knadh/listmonk#300 (although I am not using listmonk, only smtppool).

I only send to only one address, but there are many send requests coming in in parallel sometimes.

[peffis]

But I see also that there was a commit done - 6f93552
, which I am not using I think. Perhaps that is the fix actually and perhaps I should just upgrade

[knadh]

Yep, this issue was fixed in the last release. Please upgrade.