in store/, change functions from calling panic to returning errors

this is a library package, errors should be explicit. callers had to be careful
when calling these "X" functions. now it's explicit.

smtpserver/analyze.go

@@ -2,6 +2,7 @@ package smtpserver
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"os"
 	"time"
@@ -172,7 +173,10 @@ func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delive
 			if rs != nil {
 				mailbox = rs.Mailbox
 			}
-			mb := d.acc.MailboxFindX(tx, mailbox)
+			mb, err := d.acc.MailboxFind(tx, mailbox)
+			if err != nil {
+				return fmt.Errorf("finding destination mailbox: %w", err)
+			}
 			if mb != nil {
 				// We want to deliver to mb.ID, but this message may be rejected and sent to the
 				// Rejects mailbox instead, which MailboxID overwritten. Record the ID in
@@ -187,7 +191,6 @@ func analyze(ctx context.Context, log *mlog.Log, resolver dns.Resolver, d delive
 				log.Debug("mailbox not found in database", mlog.Field("mailbox", mailbox))
 			}
 
-			var err error
 			isjunk, conclusive, method, err = reputation(tx, log, d.m)
 			reason = string(method)
 			return err

smtpserver/server.go

@@ -577,7 +577,7 @@ func serve(listenerName string, cid int64, hostname dns.Domain, tlsConfig *tls.C
 		} else if err, ok := x.(error); ok && isClosed(err) {
 			c.log.Infox("connection closed", err)
 		} else {
-			c.log.Error("unhandled error", mlog.Field("err", x))
+			c.log.Error("unhandled panic", mlog.Field("err", x))
 			debug.PrintStack()
 			metrics.PanicInc("smtpserver")
 		}
@@ -679,7 +679,7 @@ func command(c *conn) {
 		} else {
 			// Other type of panic, we pass it on, aborting the connection.
 			c.log.Errorx("command panic", err)
-			panic(x)
+			panic(err)
 		}
 	}()