diff -ru courier-authlib-0.52/authvchkpw.c courier-authlib-0.52-apop/authvchkpw.c
--- courier-authlib-0.52/authvchkpw.c	2004-11-14 11:58:16.000000000 +0900
+++ courier-authlib-0.52-apop/authvchkpw.c	2005-01-04 20:01:49.000000000 +0900
@@ -100,7 +100,7 @@
 	*/
 
 #ifdef HAVE_OPEN_SMTP_RELAY
-	if ( (strcmp("pop3", service)==0) || (strcmp("imap", service)==0) ) {
+	if ( (strcmp("pop3", service)==0) || (strcmp("imap", service)==0) || (strcmp("apop", service)==0)) {
 		/* Michael Bowe 13th August 2003
 		 *
 		 * There is a problem here because open_smtp_relay needs 
diff -ru courier-authlib-0.52/checkpassword.c courier-authlib-0.52-apop/checkpassword.c
--- courier-authlib-0.52/checkpassword.c	2004-10-21 09:10:49.000000000 +0900
+++ courier-authlib-0.52-apop/checkpassword.c	2005-01-04 20:01:49.000000000 +0900
@@ -37,6 +37,7 @@
 #if	HAVE_MD5LIB
 	if (strncmp(encrypted_password, "$1$", 3) == 0
 		|| strncasecmp(encrypted_password, "{MD5}", 5) == 0
+		|| strncasecmp(encrypted_password, "{APOP}", 6) == 0
 		)
 		return (authcheckpasswordmd5(password, encrypted_password));
 #endif
diff -ru courier-authlib-0.52/checkpasswordmd5.c courier-authlib-0.52-apop/checkpasswordmd5.c
--- courier-authlib-0.52/checkpasswordmd5.c	2004-10-21 09:10:49.000000000 +0900
+++ courier-authlib-0.52-apop/checkpasswordmd5.c	2005-01-04 20:05:48.000000000 +0900
@@ -3,6 +3,8 @@
 ** distribution information.
 */
 
+#include <stdio.h>
+#include <stdlib.h>
 #if	HAVE_CONFIG_H
 #include	"courier_auth_config.h"
 #endif
@@ -27,5 +29,33 @@
 	{
                return (strcmp(encrypted_password+5, md5_hash_courier(password)));
 	}
+
+	if (strncasecmp(encrypted_password, "{APOP}", 6) == 0)
+	{
+		char *opass, *cpass, *okpass, *p, okmesg[BUFSIZ];
+		int j;
+		MD5_DIGEST digest;
+		if((opass=malloc(strlen(password)+1)) == 0)
+		{
+			perror("malloc");
+			exit(1);
+		}
+		strcpy(opass, password);
+		cpass=strtok(opass, " ");
+		p=strtok(0, "\t\r");
+		if((okpass = malloc(strlen(p)+strlen(encrypted_password)+3)) == 0)
+		{
+			perror("malloc");
+			exit(1);
+		}
+		strcat(strcpy(okpass, p), encrypted_password+6);
+		md5_digest(okpass, strlen(okpass), digest);
+		for(j=0; j<sizeof(digest); j++)
+			sprintf(&okmesg[j*2], "%02x", digest[j]);
+		free(okpass);
+		j=strcmp(cpass, okmesg);
+		free(opass);
+		return (j);
+	}
 	return (-1);
 }