diff --git a/internal/transfer/provider_pmapi.go b/internal/transfer/provider_pmapi.go
index d53a2f49..7b11f43c 100644
--- a/internal/transfer/provider_pmapi.go
+++ b/internal/transfer/provider_pmapi.go
@@ -33,8 +33,8 @@ type PMAPIProvider struct {
 	addressID     string
 	keyRing       *crypto.KeyRing
 
-	importMsgReqMap  map[string]*pmapi.ImportMsgReq // Key is msg transfer ID.
-	importMsgReqSize int
+	nextImportRequests     map[string]*pmapi.ImportMsgReq // Key is msg transfer ID.
+	nextImportRequestsSize int
 
 	timeIt *timeIt
 }
@@ -47,8 +47,8 @@ func NewPMAPIProvider(config *pmapi.ClientConfig, clientManager ClientManager, u
 		userID:        userID,
 		addressID:     addressID,
 
-		importMsgReqMap:  map[string]*pmapi.ImportMsgReq{},
-		importMsgReqSize: 0,
+		nextImportRequests:     map[string]*pmapi.ImportMsgReq{},
+		nextImportRequestsSize: 0,
 
 		timeIt: newTimeIt("pmapi"),
 	}
diff --git a/internal/transfer/provider_pmapi_target.go b/internal/transfer/provider_pmapi_target.go
index 579ae61e..87e25eae 100644
--- a/internal/transfer/provider_pmapi_target.go
+++ b/internal/transfer/provider_pmapi_target.go
@@ -33,7 +33,7 @@ import (
 const (
 	pmapiImportBatchMaxItems = 10
 	pmapiImportBatchMaxSize  = 25 * 1000 * 1000 // 25 MB
-	pmapiImportWorkers       = 5
+	pmapiImportWorkers       = 4                // To keep memory under 1 GB.
 )
 
 // DefaultMailboxes returns the default mailboxes for default rules if no other is found.
@@ -79,11 +79,11 @@ func (p *PMAPIProvider) TransferFrom(rules transferRules, progress *Progress, ch
 
 	// Cache has to be cleared before each transfer to not contain
 	// old stuff from previous cancelled run.
-	p.importMsgReqMap = map[string]*pmapi.ImportMsgReq{}
-	p.importMsgReqSize = 0
+	p.nextImportRequests = map[string]*pmapi.ImportMsgReq{}
+	p.nextImportRequestsSize = 0
 
-	importMsgReqMapCh := make(chan map[string]*pmapi.ImportMsgReq)
-	wg := p.runImporting(progress, importMsgReqMapCh)
+	preparedImportRequestsCh := make(chan map[string]*pmapi.ImportMsgReq)
+	wg := p.startImportWorkers(progress, preparedImportRequestsCh)
 
 	for msg := range ch {
 		if progress.shouldStop() {
@@ -93,14 +93,14 @@ func (p *PMAPIProvider) TransferFrom(rules transferRules, progress *Progress, ch
 		if p.isMessageDraft(msg) {
 			p.transferDraft(rules, progress, msg)
 		} else {
-			p.transferMessage(rules, progress, msg, importMsgReqMapCh)
+			p.transferMessage(rules, progress, msg, preparedImportRequestsCh)
 		}
 	}
 
-	if len(p.importMsgReqMap) > 0 {
-		importMsgReqMapCh <- p.importMsgReqMap
+	if len(p.nextImportRequests) > 0 {
+		preparedImportRequestsCh <- p.nextImportRequests
 	}
-	close(importMsgReqMapCh)
+	close(preparedImportRequestsCh)
 	wg.Wait()
 }
 
@@ -170,7 +170,7 @@ func (p *PMAPIProvider) importDraft(msg Message, globalMailbox *Mailbox) (string
 	return draft.ID, nil
 }
 
-func (p *PMAPIProvider) transferMessage(rules transferRules, progress *Progress, msg Message, importMsgReqMapCh chan map[string]*pmapi.ImportMsgReq) {
+func (p *PMAPIProvider) transferMessage(rules transferRules, progress *Progress, msg Message, preparedImportRequestsCh chan map[string]*pmapi.ImportMsgReq) {
 	importMsgReq, err := p.generateImportMsgReq(msg, rules.globalMailbox)
 	if err != nil {
 		progress.messageImported(msg.ID, "", err)
@@ -178,13 +178,13 @@ func (p *PMAPIProvider) transferMessage(rules transferRules, progress *Progress,
 	}
 
 	importMsgReqSize := len(importMsgReq.Body)
-	if p.importMsgReqSize+importMsgReqSize > pmapiImportBatchMaxSize || len(p.importMsgReqMap) == pmapiImportBatchMaxItems {
-		importMsgReqMapCh <- p.importMsgReqMap
-		p.importMsgReqMap = map[string]*pmapi.ImportMsgReq{}
-		p.importMsgReqSize = 0
+	if p.nextImportRequestsSize+importMsgReqSize > pmapiImportBatchMaxSize || len(p.nextImportRequests) == pmapiImportBatchMaxItems {
+		preparedImportRequestsCh <- p.nextImportRequests
+		p.nextImportRequests = map[string]*pmapi.ImportMsgReq{}
+		p.nextImportRequestsSize = 0
 	}
-	p.importMsgReqMap[msg.ID] = importMsgReq
-	p.importMsgReqSize += importMsgReqSize
+	p.nextImportRequests[msg.ID] = importMsgReq
+	p.nextImportRequestsSize += importMsgReqSize
 }
 
 func (p *PMAPIProvider) generateImportMsgReq(msg Message, globalMailbox *Mailbox) (*pmapi.ImportMsgReq, error) {
@@ -276,13 +276,13 @@ func computeMessageFlags(labels []string) (flag int64) {
 	return flag
 }
 
-func (p *PMAPIProvider) runImporting(progress *Progress, importMsgReqMapCh chan map[string]*pmapi.ImportMsgReq) *sync.WaitGroup {
+func (p *PMAPIProvider) startImportWorkers(progress *Progress, preparedImportRequestsCh chan map[string]*pmapi.ImportMsgReq) *sync.WaitGroup {
 	var wg sync.WaitGroup
+	wg.Add(pmapiImportWorkers)
 	for i := 0; i < pmapiImportWorkers; i++ {
-		wg.Add(1)
 		go func() {
-			for importMsgReqMap := range importMsgReqMapCh {
-				p.importMessages(progress, importMsgReqMap)
+			for importRequests := range preparedImportRequestsCh {
+				p.importMessages(progress, importRequests)
 			}
 			wg.Done()
 		}()
@@ -290,14 +290,14 @@ func (p *PMAPIProvider) runImporting(progress *Progress, importMsgReqMapCh chan
 	return &wg
 }
 
-func (p *PMAPIProvider) importMessages(progress *Progress, importMsgReqMap map[string]*pmapi.ImportMsgReq) {
+func (p *PMAPIProvider) importMessages(progress *Progress, importRequests map[string]*pmapi.ImportMsgReq) {
 	if progress.shouldStop() {
 		return
 	}
 
 	importMsgIDs := []string{}
 	importMsgRequests := []*pmapi.ImportMsgReq{}
-	for msgID, req := range importMsgReqMap {
+	for msgID, req := range importRequests {
 		importMsgIDs = append(importMsgIDs, msgID)
 		importMsgRequests = append(importMsgRequests, req)
 	}
@@ -307,7 +307,7 @@ func (p *PMAPIProvider) importMessages(progress *Progress, importMsgReqMap map[s
 	// In case the whole request failed, try to import every message one by one.
 	if err != nil || len(results) == 0 {
 		log.WithError(err).Warning("Importing messages failed, trying one by one")
-		for msgID, req := range importMsgReqMap {
+		for msgID, req := range importRequests {
 			importedID, err := p.importMessage(msgID, progress, req)
 			progress.messageImported(msgID, importedID, err)
 		}