diff --git a/go.mod b/go.mod
index 26ec7a6..1d0da4c 100644
--- a/go.mod
+++ b/go.mod
@@ -15,7 +15,7 @@ require (
 	github.com/knadh/go-pop3 v0.3.0
 	github.com/knadh/goyesql/v2 v2.1.2
 	github.com/knadh/koanf v1.2.3
-	github.com/knadh/smtppool v1.0.0
+	github.com/knadh/smtppool v1.0.1
 	github.com/knadh/stuffbin v1.1.0
 	github.com/labstack/echo/v4 v4.9.0
 	github.com/lib/pq v1.10.3
diff --git a/go.sum b/go.sum
index a29a35e..bffce65 100644
--- a/go.sum
+++ b/go.sum
@@ -84,6 +84,8 @@ github.com/knadh/koanf v1.2.3 h1:2Rkr0YhhYk+4QEOm800Q3Pu0Wi87svTxM6uuEb4WhYw=
 github.com/knadh/koanf v1.2.3/go.mod h1:xpPTwMhsA/aaQLAilyCCqfpEiY1gpa160AiCuWHJUjY=
 github.com/knadh/smtppool v1.0.0 h1:1c8A7+nD8WdMMzvd3yY5aoY9QBgyGTA+Iq1IdlgKGJw=
 github.com/knadh/smtppool v1.0.0/go.mod h1:3DJHouXAgPDBz0kC50HukOsdapYSwIEfJGwuip46oCA=
+github.com/knadh/smtppool v1.0.1 h1:gNASLB4x4W5jhVHRApwr9d2xSpsuannAFJVt/bVR8pA=
+github.com/knadh/smtppool v1.0.1/go.mod h1:3DJHouXAgPDBz0kC50HukOsdapYSwIEfJGwuip46oCA=
 github.com/knadh/stuffbin v1.1.0 h1:f5S5BHzZALjuJEgTIOMC9NidEnBJM7Ze6Lu1GHR/lwU=
 github.com/knadh/stuffbin v1.1.0/go.mod h1:yVCFaWaKPubSNibBsTAJ939q2ABHudJQxRWZWV5yh+4=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
diff --git a/internal/messenger/email/email.go b/internal/messenger/email/email.go
index cbbd513..90a41f8 100644
--- a/internal/messenger/email/email.go
+++ b/internal/messenger/email/email.go
@@ -11,7 +11,10 @@ import (
 	"github.com/knadh/smtppool"
 )
 
-const emName = "email"
+const (
+	emName        = "email"
+	hdrReturnPath = "Return-Path"
+)
 
 // Server represents an SMTP server's credentials.
 type Server struct {
@@ -125,16 +128,22 @@ func (e *Emailer) Push(m messenger.Message) error {
 	}
 
 	em.Headers = textproto.MIMEHeader{}
-	// Attach e-mail level headers.
-	if len(m.Headers) > 0 {
-		em.Headers = m.Headers
-	}
 
 	// Attach SMTP level headers.
-	if len(srv.EmailHeaders) > 0 {
-		for k, v := range srv.EmailHeaders {
-			em.Headers.Set(k, v)
-		}
+	for k, v := range srv.EmailHeaders {
+		em.Headers.Set(k, v)
+	}
+
+	// Attach e-mail level headers.
+	for k, v := range m.Headers {
+		em.Headers.Set(k, v[0])
+	}
+
+	// If the `Return-Path` header is set, it should be set as the
+	// the SMTP envelope sender (via the Sender field of the email struct).
+	if sender := em.Headers.Get(hdrReturnPath); sender != "" {
+		em.Sender = sender
+		em.Headers.Del(hdrReturnPath)
 	}
 
 	switch m.ContentType {